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; **************************************

; *** SPECTRUM 128 ROM 0 DISASSEMBLY ***

; **************************************

; The Spectrum ROMs are copyright Amstrad, who have kindly given permission

; to reverse engineer and publish Spectrum ROM disassemblies.

; =====

; NOTES

; =====

; ------------

; Release Date

; ------------

; 4th November 2010

; ------------------------

; Disassembly Contributors

; ------------------------

; Matthew Wilson  (www.matthew-wilson.net/spectrum/rom/)

; Andrew Owen     (cheveron-AT-gmail.com)

; Geoff Wearmouth (gwearmouth-AT-hotmail.com)

; Rui Tunes

; Paul Farrow     (www.fruitcake.plus.com)

; -------

; Markers

; -------

; The following markers appear throughout the disassembly:

;

; [...] = Indicates a comment about the code.

; ????  = Information to be determined.

;

; For bugs, the following marker format is used:

;

; [*BUG* - xxxx. Credit: yyyy]  = Indicates a confirmed bug, with a description 'xxxx' of it and the discoverer 'yyyy'.

; [*BUG*? - xxxx. Credit: yyyy] = Indicates a suspected bug, with a description 'xxxx' of it and the discoverer 'yyyy'.

;

; Since many of the Spectrum 128 ROM routines were re-used in the Spectrum +2 and +3, where a bug was originally identified

; in the Spectrum +2 or +3 the discoverer is acknowledged along with who located the corresponding bug in the Spectrum 128.

;

; For every bug identified, an example fix is provided and the author acknowledged. Some of these fixes can be made directly within the routines

; affected since they do not increase the length of those routines. Others require the insertion of extra instructions and hence these cannot be

; completely fitted within the routines affected. Instead a jump must be made to a patch routine located within a spare area of the ROM.

; Fortunately there is 0.5K of unused routines located at $2336-$2536 (ROM 0) which are remnants of the original Spanish 128, and another unused routine

; located at $3FC3-$3FCE (ROM 0). This is sufficient space to implement all of the bug fixes suggested.

; =================

; ASSEMBLER DEFINES

; =================

;TASM directives:

;#DEFINE DB .BYTE

;#DEFINE DEFW .WORD

;#DEFINE DEFM .TEXT

;#DEFINE DEFS .FILL

;#DEFINE END  .END

;#DEFINE EQU  .EQU

;#DEFINE ORG  .ORG

; ==============================

; REFERENCE INFORMATION - PART 1

; ==============================

; ==========================

; 128 BASIC Mode Limitations

; ==========================

; There are a number of limitations when using 128 BASIC mode, some of which are not present when using the equivalent 48 BASIC mode operations.

; These are more design decisions than bugs.

;

; - The RAM disk VERIFY command does not verify but simply performs a LOAD.

; - The renumber facility will not renumber line numbers that are defined as an expression, e.g. GO TO VAL "10".

; - The printer output routine cannot handle binary data and hence EPSON printer ESC codes cannot be sent.

; - The Editor has the following limitations:

;   - Variables cannot have the same name as a keyword. This only applies when entering a program and not when one is loaded in.

;   - Line number 0 is not supported and will not list properly. It is not possible to directly insert such a line, not even in 48 BASIC mode,

;     and so line number 0 is not officially supported.

;   - There is a practical limitation on the size of lines that can be entered. It is limited to 20 indented rows, which is the size of the editing buffers.

;     Typed lines greater than 20 rows get inserted into the BASIC program, but only the first 20 rows are shown on screen. Editing such a line causes

;     it to be truncated to 20 rows. There is no warning when the 20 row limit is exceeded.

;   - It is not possible to directly enter embedded control codes, or to correctly edit loaded in programs that contain them. Loaded programs that

;     contain them will run correctly so long as the lines are not edited.

;   - It is not possible to embed the string of characters ">=", "<=" or "<>" into a string or REM statement without them being tokenized

;     (this is perhaps more an oversight than a design decision).

;   - In 48 BASIC mode if the line '10 REM abc: PRINT xyz' is typed then the word PRINT is stored as a new keyword since the colon (arguably incorrectly)

;     reverts to 'K' mode. In 128 BASIC mode, typing the same line stores each letter as a separate character.

; ==================

; Timing Information

; ==================

; Clock Speed   = 3.54690 MHz (48K Spectrum clock speed was 3.50000 MHz)

; Scan line     = 228 T-states (48K Spectrum was 224 T-states).

; TV scan lines = 311 total, 63 above picture (48K Spectrum had 312 total, 64 above picture).

; ===========

; I/O Details

; ===========

; -------------

; Memory Paging

; -------------

; Memory paging is controlled by I/O port:

; $7FFD (Out) - Bits 0-2: RAM bank (0-7) to page into memory map at $C000.

;               Bit 3   : 0=SCREEN 0 (normal display file in bank 5), 1=SCREEN 1 (shadow display file in bank 7).

;               Bit 4   : 0=ROM 0 (128K Editor), 1=ROM 1 (48K BASIC).

;               Bit 5   : 1=Disable further output to this port until a hard reset occurs.

;               Bit 6-7 : Not used (always write 0).

;

; The Editor ROM (ROM 0) always places a copy of the last value written to port $7FFD

; into new system variable BANK_M ($5B5C).

;

; ----------

; Memory Map

; ----------

; ROM 0 or 1 resides at $0000-$3FFF.

; RAM bank 5 resides at $4000-$7FFF always.

; RAM bank 2 resides at $8000-$BFFF always.

; Any RAM bank may reside at $C000-$FFFF.

;

; -------------------

; Shadow Display File

; -------------------

; The shadow screen may be active even when not paged into the memory map.

;

; ----------------

; Contended Memory

; ----------------

; Physical RAM banks 1, 3, 5 and 7 are contended with the ULA.

;

; -----------------

; Logical RAM Banks

; -----------------

; Throughout ROM 0, memory banks are accessed using a logical numbering scheme, which

; maps to physical RAM banks as follows:

;

; Logical Bank   Physical Bank

; ------------   -------------

;     $00             $01

;     $01             $03

;     $02             $04

;     $03             $06

;     $04             $07

;     $05             $00

;

; This scheme makes the RAM disk code simpler than having to deal directly with physical RAM bank numbers.

; -------------------------

; AY-3-8912 Sound Generator

; -------------------------

; The AY-3-8912 sound generator is controlled by two I/O ports:

; $FFFD (Out)    - Select a register 0-14.

; $FFFD (In)     - Read from the selected register.

; $BFFD (In/Out) - Write to the selected register. The status of the register can also be read back.

;

; The AY-3-8912 I/O port A is used to drive the RS232 and Keypad sockets.

;

; Register       Function                        Range

; --------       --------                        -----

; 0              Channel A fine pitch            8-bit (0-255)

; 1              Channel A course pitch          4-bit (0-15)

; 2              Channel B fine pitch            8-bit (0-255)

; 3              Channel B course pitch          4-bit (0-15)

; 4              Channel C fine pitch            8-bit (0-255)

; 5              Channel C course pitch          4-bit (0-15)

; 6              Noise pitch                     5-bit (0-31)

; 7              Mixer                           8-bit (see end of file for description)

; 8              Channel A volume                4-bit (0-15, see end of file for description)

; 9              Channel B volume                4-bit (0-15, see end of file for description)

; 10             Channel C volume                4-bit (0-15, see end of file for description)

; 11             Envelope fine duration          8-bit (0-255)

; 12             Envelope course duration        8-bit (0-255)

; 13             Envelope shape                  4-bit (0-15)

; 14             I/O port A                      8-bit (0-255)

;

; See the end of this document for description on the sound generator registers.

;

; ----------------------------------

; I/O Port A (AY-3-8912 Register 14)

; ----------------------------------

; This controls the RS232 and Keypad sockets.

; Select the port via a write to port $FFFD with 14, then read via port $FFFD and write via port $BFFD. The state of port $BFFD can also be read back.

;

; Bit 0: KEYPAD CTS (out) - 0=Spectrum ready to receive, 1=Busy

; Bit 1: KEYPAD RXD (out) - 0=Transmit high bit,         1=Transmit low bit

; Bit 2: RS232  CTS (out) - 0=Spectrum ready to receive, 1=Busy

; Bit 3: RS232  RXD (out) - 0=Transmit high bit,         1=Transmit low bit

; Bit 4: KEYPAD DTR (in)  - 0=Keypad ready for data,     1=Busy

; Bit 5: KEYPAD TXD (in)  - 0=Receive high bit,          1=Receive low bit

; Bit 6: RS232  DTR (in)  - 0=Device ready for data,     1=Busy

; Bit 7: RS232  TXD (in)  - 0=Receive high bit,          1=Receive low bit

;

; See the end of this document for the pinouts for the RS232 and KEYPAD sockets.

; ------------------

; Standard I/O Ports

; ------------------

; See the end of this document for descriptions of the standard Spectrum I/O ports.

; ==================

; Error Report Codes

; ==================

; ---------------------------

; Standard Error Report Codes

; ---------------------------

; See the end of this document for descriptions of the standard error report codes.

; ----------------------

; New Error Report Codes

; ----------------------

; a - MERGE error                      MERGE! would not execute for some reason - either size or file type wrong.

; b - Wrong file type                  A file of an inappropriate type was specified during RAM disk operation, for instance a CODE file in LOAD!"name".

; c - CODE error                       The size of the file would lead to an overrun of the top of memory.

; d - Too many brackets                Too many brackets around a repeated phrase in one of the arguments.

; e - File already exists              The file name specified has already been used.

; f - Invalid name                     The file name specified is empty or above 10 characters in length.

; g - File does not exist              [Never used by the ROM].

; h - File does not exist              The specified file could not be found.

; i - Invalid device                   The device name following the FORMAT command does not exist or correspond to a physical device.

; j - Invalid baud rate                The baud rate for the RS232 was set to 0.

; k - Invalid note name                PLAY came across a note or command it didn't recognise, or a command which was in lower case.

; l - Number too big                   A parameter for a command is an order of magnitude too big.

; m - Note out of range                A series of sharps or flats has taken a note beyond the range of the sound chip.

; n - Out of range                     A parameter for a command is too big or too small. If the error is very large, error L results.

; o - Too many tied notes              An attempt was made to tie too many notes together.

; p - (c) 1986 Sinclair Research Ltd   This error is given when too many PLAY channel strings are specified. Up to 8 PLAY channel strings are supported

;                                      by MIDI devices such as synthesisers, drum machines or sequencers. Note that a PLAY command with more than 8 strings

;                                      cannot be entered directly from the Editor. The Spanish 128 produces "p Bad parameter" for this error. It could be

;                                      that the intention was to save memory by using the existing error message of "Q Parameter error" but the change of report

;                                      code byte was overlooked.

; ================

; System Variables

; ================

; --------------------

; New System Variables

; --------------------

; These are held in the old ZX Printer buffer at $5B00-$5BFF.

; Note that some of these names conflict with the system variables used by the ZX Interface 1.

SWAP        EQU $5B00  ; 20   Swap paging subroutine.

YOUNGER     EQU $5B14  ;  9   Return paging subroutine.

ONERR       EQU $5B1D  ; 18   Error handler paging subroutine.

PIN         EQU $5B2F  ;  5   RS232 input pre-routine.

POUT        EQU $5B34  ; 22   RS232 token output pre-routine. This can be patched to bypass the control code filter.

POUT2       EQU $5B4A  ; 14   RS232 character output pre-routine.

TARGET      EQU $5B58  ;  2   Address of subroutine to call in ROM 1.

RETADDR     EQU $5B5A  ;  2   Return address in ROM 0.

BANK_M      EQU $5B5C  ;  2   Copy of last byte output to I/O port $7FFD.

RAMRST      EQU $5B5D  ;  1   Stores instruction RST $08 and used to produce a standard ROM error. Changing this instruction allows 128 BASIC to be extended (see end of this document for details).

RAMERR      EQU $5B5E  ;  1   Error number for use by RST $08 held in RAMRST.

BAUD        EQU $5B5F  ;  2   Baud rate timing constant for RS232 socket. Default value of 11. [Name clash with ZX Interface 1 system variable at $5CC3]

SERFL       EQU $5B61  ;  2   Second character received flag:

                       ;        Bit 0   : 1=Character in buffer.

                       ;        Bits 1-7: Not used (always hold 0).

              ; $5B62  ;      Received Character.

COL         EQU $5B63  ;  1   Current column from 1 to WIDTH.

WIDTH       EQU $5B64  ;  1   Paper column width. Default value of 80. [Name clash with ZX Interface 1 Edition 2 system variable at $5CB1]

TVPARS      EQU $5B65  ;  1   Number of inline parameters expected by RS232 (e.g. 2 for AT).

FLAGS3      EQU $5B66  ;  1   Flags: [Name clashes with the ZX Interface 1 system variable at $5CB6]

                       ;        Bit 0: 1=BASIC/Calculator mode, 0=Editor/Menu mode.

                       ;        Bit 1: 1=Auto-run loaded BASIC program. [Set but never tested by the ROM]

                       ;        Bit 2: 1=Editing RAM disk catalogue.

                       ;        Bit 3: 1=Using RAM disk commands, 0=Using cassette commands.

                       ;        Bit 4: 1=Indicate LOAD.

                       ;        Bit 5: 1=Indicate SAVE.

                       ;        Bit 6; 1=Indicate MERGE.

                       ;        Bit 7: 1=Indicate VERIFY.

N_STR1      EQU $5B67  ; 10   Used by RAM disk to store a filename. [Name clash with ZX Interface 1 system variable at $5CDA]

                       ;      Used by the renumber routine to store the address of the BASIC line being examined.

HD_00       EQU $5B71  ;  1   Used by RAM disk to store file header information (see RAM disk Catalogue section below for details). [Name clash with ZX Interface 1 system variable at $5CE6]

                       ;      Used as column pixel counter in COPY routine.

                       ;      Used by FORMAT command to store specified baud rate.

                       ;      Used by renumber routine to store the number of digits in a pre-renumbered line number reference. [Name clash with ZX Interface 1 system variable at $5CE7]

HD_0B       EQU $5B72  ;  2   Used by RAM disk to store header info - length of block.

                       ;      Used as half row counter in COPY routine.

                       ;      Used by renumber routine to generate ASCII representation of a new line number.

HD_0D       EQU $5B74  ;  2   Used by RAM disk to store file header information (see RAM disk Catalogue section below for details). [Name clash with ZX Interface 1 system variable at $5CE9]

HD_0F       EQU $5B76  ;  2   Used by RAM disk to store file header information (see RAM disk Catalogue section below for details). [Name clash with ZX Interface 1 system variable at $5CEB]

                       ;      Used by renumber routine to store the address of a referenced BASIC line.

HD_11       EQU $5B78  ;  2   Used by RAM disk to store file header information (see RAM disk Catalogue section below for details). [Name clash with ZX Interface 1 system variable at $5CED]

                       ;      Used by renumber routine to store existing VARS address/current address within a line.

SC_00       EQU $5B7A  ;  1   Used by RAM disk to store alternate file header information (see RAM disk Catalogue section below for details).

SC_0B       EQU $5B7B  ;  2   Used by RAM disk to store alternate file header information (see RAM disk Catalogue section below for details).

SC_0D       EQU $5B7D  ;  2   Used by RAM disk to store alternate file header information (see RAM disk Catalogue section below for details).

SC_0F       EQU $5B7F  ;  2   Used by RAM disk to store alternate file header information (see RAM disk Catalogue section below for details).

OLDSP       EQU $5B81  ;  2   Stores old stack pointer when TSTACK in use.

SFNEXT      EQU $5B83  ;  2   End of RAM disk catalogue marker. Pointer to first empty catalogue entry.

SFSPACE     EQU $5B85  ;  3   Number of bytes free in RAM disk (3 bytes, 17 bit, LSB first).

ROW01       EQU $5B88  ;  1   Stores keypad data for row 3, and flags:

                       ;        Bit 0   : 1=Key '+' pressed.

                       ;        Bit 1   : 1=Key '6' pressed.

                       ;        Bit 2   : 1=Key '5' pressed.

                       ;        Bit 3   : 1=Key '4' pressed.

                       ;        Bits 4-5: Always 0.

                       ;        Bit 6   : 1=Indicates successful communications to the keypad.

                       ;        Bit 7   : 1=If communications to the keypad established.

ROW23       EQU $5B89  ;  1   Stores keypad key press data for rows 1 and 2:

                       ;        Bit 0: 1=Key ')' pressed.

                       ;        Bit 1: 1=Key '(' pressed.

                       ;        Bit 2: 1=Key '*' pressed.

                       ;        Bit 3: 1=Key '/' pressed.

                       ;        Bit 4: 1=Key '-' pressed.

                       ;        Bit 5: 1=Key '9' pressed.

                       ;        Bit 6: 1=Key '8' pressed.

                       ;        Bit 7: 1=Key '7' pressed.

ROW45       EQU $5B8A  ;  1   Stores keypad key press data for rows 4 and 5:

                       ;        Bit 0: Always 0.

                       ;        Bit 1: 1=Key '.' pressed.

                       ;        Bit 2: Always 0.

                       ;        Bit 3: 1=Key '0' pressed.

                       ;        Bit 4: 1=Key 'ENTER' pressed.

                       ;        Bit 5: 1=Key '3' pressed.

                       ;        Bit 6: 1=Key '2' pressed.

                       ;        Bit 7: 1=Key '1' pressed.

SYNRET      EQU $5B8B  ;  2   Return address for ONERR routine.

LASTV       EQU $5B8D  ;  5   Last value printed by calculator.

RNLINE      EQU $5B92  ;  2   Address of the length bytes in the line currently being renumbered.

RNFIRST     EQU $5B94  ;  2   Starting line number when renumbering. Default value of 10.

RNSTEP      EQU $5B96  ;  2   Step size when renumbering. Default value of 10.

STRIP1      EQU $5B98  ; 32   Used as RAM disk transfer buffer (32 bytes to $5BB7).

                       ;      Used to hold Sinclair stripe character patterns (16d bytes to $5BA7).

                       ;      ...

TSTACK      EQU $5BFF  ;  n   Temporary stack (grows downwards). The byte at $5BFF is not actually used.

; -------------------------

; Standard System Variables

; -------------------------

; These occupy addresses $5C00-$5CB5.

; See the end of this document for descriptions of the standard system variables.

; ------------------

; RAM Disk Catalogue

; ------------------

; The catalogue can occupy addresses $C000-$EBFF in physical RAM bank 7, starting at $EBFF and growing downwards.

;

; Each entry contains 20 bytes:

;   Bytes $00-$09: Filename.

;   Bytes $0A-$0C: Start address of file in RAM disk area.

;   Bytes $0D-$0F: Length of file in RAM disk area.

;   Bytes $10-$12: End address of file in RAM disk area (used as current position indicator when loading/saving).

;   Byte  $13    : Flags:

;                     Bit 0   : 1=Entry requires updating.

;                     Bits 1-7: Not used (always hold 0).

;

; The catalogue can store up to 562 entries, and hence the RAM disk can never hold more than 562 files no matter

; how small the files themselves are. Note that filenames are case sensitive.

;

; The shadow screen (SCREEN 1) also resides in physical RAM bank 7 and so if more than 217 catalogue

; entries are created then SCREEN 1 will become corrupted [Credit: Toni Baker, ZX Computing Monthly].

; However, since screen 1 cannot be used from BASIC, it may have been a design decision to allow the

; RAM disk to overwrite it.

;

; The actual files are stored in physical RAM banks 1, 3, 4 and 6 (logical banks 0, 1, 2, 3),

; starting from $C000 in physical RAM bank 1 and growing upwards.

;

; A file consists of a 9 byte header followed by the data for the file. The header bytes

; have the following meaning:

;   Byte  $00    : File type - $00=Program, $01=Numeric array, $02=Character array, $03=Code/Screen$.

;   Bytes $01-$02: Length of program/code block/screen$/array ($1B00 for screen$).

;   Bytes $03-$04: Start of code block/screen$ ($4000 for screen$).

;   Bytes $05-$06: Offset to the variables (i.e. length of program) if a program. For an array, $05 holds the variable name.

;   Bytes $07-$08: Auto-run line number for a program ($80 in high byte if no auto-run).

; --------------------------

; Editor Workspace Variables

; --------------------------

; These occupy addresses $EC00-$FFFF in physical RAM bank 7, and form a workspace used by 128 BASIC Editor.

;

; $EC00    3   Byte 0: Flags used when inserting a line into the BASIC program (first 4 bits are mutually exclusive).

;                Bit 0: 1=First row of the BASIC line off top of screen.

;                Bit 1: 1=On first row of the BASIC line.

;                Bit 2: 1=Using lower screen and only first row of the BASIC line visible.

;                Bit 3: 1=At the end of the last row of the BASIC line.

;                Bit 4: Not used (always 0).

;                Bit 5: Not used (always 0).

;                Bit 6: Not used (always 0).

;                Bit 7: 1=Column with cursor not yet found.

;              Byte 1: Column number of current position within the BASIC line being inserted. Used when fetching characters.

;              Byte 2: Row number of current position within the BASIC line is being inserted. Used when fetching characters.

; $EC03    3   Byte 0: Flags used upon an error when inserting a line into the BASIC program (first 4 bits are mutually exclusive).

;                Bit 0: 1=First row of the BASIC line off top of screen.

;                Bit 1: 1=On first row of the BASIC line.

;                Bit 2: 1=Using lower screen and only first row of the BASIC line visible.

;                Bit 3: 1=At the end of the last row of the BASIC line.

;                Bit 4: Not used (always 0).

;                Bit 5: Not used (always 0).

;                Bit 6: Not used (always 0).

;                Bit 7: 1=Column with cursor not yet found.

;              Byte 1: Start column number where BASIC line is being entered. Always holds 0.

;              Byte 2: Start row number where BASIC line is being entered.

; $EC06    2   Count of the number of editable characters in the BASIC line up to the cursor within the Screen Line Edit Buffer.

; $EC08    2   Version of E_PPC used by BASIC Editor to hold last line number enter.

; $EC0C    1   Current menu index.

; $EC0D    1   Flags used by 128 BASIC Editor:

;                Bit 0: 1=Screen Line Edit Buffer (including Below-Screen Line Edit Buffer) is full.

;                Bit 1: 1=Menu is displayed.

;                Bit 2: 1=Using RAM disk.

;                Bit 3: 1=Current line has been altered.

;                Bit 4: 1=Return to calculator, 0=Return to main menu.

;                Bit 5: 1=Do not process the BASIC line (used by the Calculator).

;                Bit 6: 1=Editing area is the lower screen, 0=Editing area is the main screen.

;                Bit 7: 1=Waiting for key press, 0=Got key press.

; $EC0E    1   Mode:

;                $00 = Edit Menu mode.

;                $04 = Calculator mode.

;                $07 = Tape Loader mode. [Effectively not used as overwritten by $FF]

;                $FF = Tape Loader mode.

; $EC0F    1   Main screen colours used by the 128 BASIC Editor - alternate ATTR_P.

; $EC10    1   Main screen colours used by the 128 BASIC Editor - alternate MASK_P.

; $EC11    1   Temporary screen colours used by the 128 BASIC Editor - alternate ATTR_T.

; $EC12    1   Temporary screen colours used by the 128 BASIC Editor - alternate MASK_T.

; $EC13    1   Temporary store for P_FLAG:

;                Bit 0: 1=OVER 1, 0=OVER 0.

;                Bit 1: Not used (always 0).

;                Bit 2: 1=INVERSE 1, INVERSE 0.

;                Bit 3: Not used (always 0).

;                Bit 4: 1=Using INK 9.

;                Bit 5: Not used (always 0).

;                Bit 6: 1=Using PAPER 9.

;                Bit 7: Not used (always 0).

; $EC14    1   Not used.

; $EC15    1   Holds the number of editing lines: 20 for the main screen, 1 for the lower screen.

; $EC16  735   Screen Line Edit Buffer. This represents the text on screen that can be edited. It holds 21 rows,

;              with each row consisting of 32 characters followed by 3 data bytes. Areas of white

;              space that do not contain any editable characters (e.g. the indent that starts subsequent

;              rows of a BASIC line) contain the value $00.

;                Data Byte 0:

;                  Bit 0: 1=The first row of the BASIC line.

;                  Bit 1: 1=Spans onto next row.

;                  Bit 2: Not used (always 0).

;                  Bit 3: 1=The last row of the BASIC line.

;                  Bit 4: 1=Associated line number stored.

;                  Bit 5: Not used (always 0).

;                  Bit 6: Not used (always 0).

;                  Bit 7: Not used (always 0).

;                Data Bytes 1-2: Line number of corresponding BASIC line (stored for the first row of the BASIC line only, holds $0000).

; $EEF5    1   Flags used when listing the BASIC program:

;                Bit 0   : 0=Not on the current line, 1=On the current line.

;                Bit 1   : 0=Previously found the current line, 1=Not yet found the current line.

;                Bit 2   : 0=Enable display file updates, 1=Disable display file updates.

;                Bits 3-7: Not used (always 0).

; $EEF6    1   Store for temporarily saving the value of TVFLAG.

; $EEF7    1   Store for temporarily saving the value of COORDS.

; $EEF9    1   Store for temporarily saving the value of P_POSN.

; $EEFA    2   Store for temporarily saving the value of PRCC.

; $EEFC    2   Store for temporarily saving the value of ECHO_E.

; $EEFE    2   Store for temporarily saving the value of DF_CC.

; $EF00    2   Store for temporarily saving the value of DF_CCL.

; $EF01    1   Store for temporarily saving the value of S_POSN.

; $EF03    2   Store for temporarily saving the value of SPOSNL.

; $EF05    1   Store for temporarily saving the value of SCR_CT.

; $EF06    1   Store for temporarily saving the value of ATTR_P.

; $EF07    1   Store for temporarily saving the value of MASK_P.

; $EF08    1   Store for temporarily saving the value of ATTR_T.

; $EF09 1512   Used to store screen area (12 rows of 14 columns) where menu will be shown.

;              The rows are stored one after the other, with each row consisting of the following:

;                - 8 lines of 14 display file bytes.

;                - 14 attribute file bytes.

; $F4F1-$F6E9  Not used. 505d bytes.

; $F6EA    2   The jump table address for the current menu.

; $F6EC    2   The text table address for the current menu.

; $F6EE    1   Cursor position info - Current row number.

; $F6EF    1   Cursor position info - Current column number.

; $F6F0    1   Cursor position info - Preferred column number. Holds the last user selected column position. The Editor will attempt to

;              place the cursor on this column when the user moves up or down to a new line.

; $F6F1    1   Edit area info - Top row threshold for scrolling up.

; $F6F2    1   Edit area info - Bottom row threshold for scrolling down.

; $F6F3    1   Edit area info - Number of rows in the editing area.

; $F6F4    1   Flags used when deleting:

;                Bit 0   : 1=Deleting on last row of the BASIC line, 0=Deleting on row other than the last row of the BASIC line.

;                Bits 1-7: Not used (always 0).

; $F6F5    1   Number of rows held in the Below-Screen Line Edit Buffer.

; $F6F6    2   Intended to point to the next location to access within the Below-Screen Line Edit Buffer, but incorrectly initialised to $0000 by the routine at $30D6 (ROM 0) and then never used.

; $F6F8  735   Below-Screen Line Edit Buffer. Holds the remainder of a BASIC line that has overflowed off the bottom of the Screen Line Edit Buffer. It can hold 21 rows, with each row

;              consisting of 32 characters followed by 3 data bytes. Areas of white space that do not contain any editable characters (e.g. the indent that starts subsequent rows of a BASIC line)

;              contain the value $00.

;                Data Byte 0:

;                  Bit 0: 1=The first row of the BASIC line.

;                  Bit 1: 1=Spans onto next row.

;                  Bit 2: Not used (always 0).

;                  Bit 3: 1=The last row of the BASIC line.

;                  Bit 4: 1=Associated line number stored.

;                  Bit 5: Not used (always 0).

;                  Bit 6: Not used (always 0).

;                  Bit 7: Not used (always 0).

;                Data Bytes 1-2: Line number of corresponding BASIC line (stored for the first row of the BASIC line only, holds $0000).

; $F9D7    2   Line number of the BASIC line in the program area being edited (or $0000 for no line).

; $F9DB    1   Number of rows held in the Above-Screen Line Edit Buffer.

; $F9DC    2   Points to the next location to access within the Above-Screen Line Edit Buffer.

; $F9DE  700   Above-Screen Line Edit Buffer. Holds the rows of a BASIC line that has overflowed off the top of the Screen Line Edit Buffer.

;              It can hold 20 rows, with each row consisting of 32 characters followed by 3 data bytes. Areas of white space that do not

;              contain any editable characters (e.g. the indent that starts subsequent rows of a BASIC line) contain the value $00.

;                Data Byte 0:

;                  Bit 0: 1=The first row of the BASIC line.

;                  Bit 1: 1=Spans onto next row.

;                  Bit 2: Not used (always 0).

;                  Bit 3: 1=The last row of the BASIC line.

;                  Bit 4: 1=Associated line number stored.

;                  Bit 5: Not used (always 0).

;                  Bit 6: Not used (always 0).

;                  Bit 7: Not used (always 0).

;                Data Bytes 1-2: Line number of corresponding BASIC line (stored for the first row of the BASIC line only, holds $0000).

; $FC9A    2   The line number at the top of the screen, or $0000 for the first line.

; $FC9E    1   $00=Print a leading space when constructing keyword.

; $FC9F    2   Address of the next character to fetch within the BASIC line in the program area, or $0000 for no next character.

; $FCA1    2   Address of the next character to fetch from the Keyword Construction Buffer, or $0000 for no next character.

; $FCA3   11   Keyword Construction Buffer. Holds either a line number or keyword string representation.

; $FCAE-$FCFC  Construct a BASIC Line routine.                       <<< RAM routine - See end of file for description >>>

; $FCFD-$FD2D  Copy String Into Keyword Construction Buffer routine. <<< RAM routine - See end of file for description >>>

; $FD2E-$FD69  Identify Character Code of Token String routine.      <<< RAM routine - See end of file for description >>>

; $FD6A    1   Flags used when shifting BASIC lines within edit buffer rows [Redundant]:

;                Bit 0  : 1=Set to 1 but never reset or tested. Possibly intended to indicate the start of a new BASIC line and hence whether indentation required.

;                Bit 1-7: Not used (always 0).

; $FD6B    1   The number of characters to indent subsequent rows of a BASIC line by.

; $FD6C    1   Cursor settings (indexed by IX+$00) - initialised to $00, but never used.

; $FD6D    1   Cursor settings (indexed by IX+$01) - number of rows above the editing area.

; $FD6E    1   Cursor settings (indexed by IX+$02) - initialised to $00 (when using lower screen) or $14 (when using main screen), but never subsequently used.

; $FD6F    1   Cursor settings (indexed by IX+$03) - initialised to $00, but never subsequently used.

; $FD70    1   Cursor settings (indexed by IX+$04) - initialised to $00, but never subsequently used.

; $FD71    1   Cursor settings (indexed by IX+$05) - initialised to $00, but never subsequently used.

; $FD72    1   Cursor settings (indexed by IX+$06) - attribute colour.

; $FD73    1   Cursor settings (indexed by IX+$07) - screen attribute where cursor is displayed.

; $FD74    9   The Keyword Conversion Buffer holding text to examine to see if it is a keyword.

; $FD7D    2   Address of next available location within the Keyword Conversion Buffer.

; $FD7F    2   Address of the space character between words in the Keyword Conversion Buffer.

; $FD81    1   Keyword Conversion Buffer flags, used when tokenizing a BASIC line:

;                Bit 0   : 1=Buffer contains characters.

;                Bit 1   : 1=Indicates within quotes.

;                Bit 2   : 1=Indicates within a REM.

;                Bits 3-7: Not used (always reset to 0).

; $FD82    2   Address of the position to insert the next character within the BASIC line workspace. The BASIC line

;              is created at the spare space pointed to by E_LINE.

; $FD84    1   BASIC line insertion flags, used when inserting a characters into the BASIC line workspace:

;                Bit 0   : 1=The last character was a token.

;                Bit 1   : 1=The last character was a space.

;                Bits 2-7: Not used (always 0).

; $FD85    2   Count of the number of characters in the typed BASIC line being inserted.

; $FD87    2   Count of the number of characters in the tokenized version of the BASIC line being inserted.

; $FD89    1   Holds '<' or '>' if this was the previously examined character during tokenization of a BASIC line, else $00.

; $FD8A    1   Locate Error Marker flag, holding $01 is a syntax error was detected on the BASIC line being inserted and the equivalent position within

;              the typed BASIC line needs to be found with, else it holds $00 when tokenizing a BASIC line.

; $FD8B    2   Stores the stack pointer for restoration upon an insertion error into the BASIC line workspace.

; $FD8C-$FF23  Not used. 408 bytes.

; $FF24    2   Never used. An attempt is made to set it to $EC00. This is a remnant from the Spanish 128, which stored the address of the Screen Buffer here.

;              The value is written to RAM bank 0 instead of RAM bank 7, and the value never subsequently accessed.

; $FF26    2   Not used.

; $FF28-$FF60  Not used. On the Spanish 128 this memory holds a routine that copies a character into the display file. The code to copy to routine into RAM,

;              and the routine itself are present in ROM 0 but are never executed. <<< RAM routine - See end of file for description >>>

; $FF61-$FFFF  Not used. 159 bytes.

; ========================

; Called ROM 1 Subroutines

; ========================

ERROR_1     EQU $0008

PRINT_A_1   EQU $0010

GET_CHAR    EQU $0018

NEXT_CHAR   EQU $0020

BC_SPACES   EQU $0030

TOKENS      EQU $0095

BEEPER      EQU $03B5

BEEP        EQU $03F8

SA_ALL      EQU $075A

ME_CONTRL   EQU $08B6

SA_CONTROL  EQU $0970

PRINT_OUT   EQU $09F4

PO_T_UDG    EQU $0B52

PO_MSG      EQU $0C0A

TEMPS       EQU $0D4D

CLS         EQU $0D6B

CLS_LOWER   EQU $0D6E

CL_ALL      EQU $0DAF

CL_ATTR     EQU $0E88

CL_ADDR     EQU $0E9B

CLEAR_PRB   EQU $0EDF

ADD_CHAR    EQU $0F81

ED_ERROR    EQU $107F

CLEAR_SP    EQU $1097

KEY_INPUT   EQU $10A8

KEY_M_CL    EQU $10DB

MAIN_4      EQU $1303

ERROR_MSGS  EQU $1391

MESSAGES    EQU $1537

REPORT_J    EQU $15C4

OUT_CODE    EQU $15EF

CHAN_OPEN   EQU $1601

CHAN_FLAG   EQU $1615

POINTERS    EQU $1664

CLOSE       EQU $16E5

MAKE_ROOM   EQU $1655

LINE_NO     EQU $1695

SET_MIN     EQU $16B0

SET_WORK    EQU $16BF

SET_STK     EQU $16C5

OPEN        EQU $1736

LIST_5      EQU $1822

NUMBER      EQU $18B6

LINE_ADDR   EQU $196E

EACH_STMT   EQU $198B

NEXT_ONE    EQU $19B8

RECLAIM     EQU $19E5

RECLAIM_2   EQU $19E8

E_LINE_NO   EQU $19FB

OUT_NUM_1   EQU $1A1B

CLASS_01    EQU $1C1F

VAL_FET_1   EQU $1C56

CLASS_04    EQU $1C6C

EXPT_2NUM   EQU $1C7A

EXPT_1NUM   EQU $1C82

EXPT_EXP    EQU $1C8C

CLASS_09    EQU $1CBE

FETCH_NUM   EQU $1CDE

USE_ZERO    EQU $1CE6

STOP        EQU $1CEE

F_REORDER   EQU $1D16

LOOK_PROG   EQU $1D86

NEXT        EQU $1DAB

PASS_BY     EQU $1E39

RESTORE     EQU $1E42

REST_RUN    EQU $1E45

RANDOMIZE   EQU $1E4F

CONTINUE    EQU $1E5F

GO_TO       EQU $1E67

COUT        EQU $1E7A     ; Should be OUT but renamed since some assemblers detect this as an instruction.

POKE        EQU $1E80

FIND_INT2   EQU $1E99

TEST_ROOM   EQU $1F05

PAUSE       EQU $1F3A

PRINT_2     EQU $1FDF

PR_ST_END   EQU $2048

STR_ALTER   EQU $2070

INPUT_1     EQU $2096

IN_ITEM_1   EQU $20C1

CO_TEMP_4   EQU $21FC

BORDER      EQU $2294

PIXEL_ADDR  EQU $22AA

PLOT        EQU $22DC

PLOT_SUB    EQU $22E5

CIRCLE      EQU $2320

DR_3_PRMS   EQU $238D

LINE_DRAW   EQU $2477

SCANNING    EQU $24FB

SYNTAX_Z    EQU $2530

LOOK_VARS   EQU $28B2

STK_VAR     EQU $2996

STK_FETCH   EQU $2BF1

D_RUN       EQU $2C15

ALPHA       EQU $2C8D

NUMERIC     EQU $2D1B

STACK_BC    EQU $2D2B

FP_TO_BC    EQU $2DA2

PRINT_FP    EQU $2DE3

HL_MULT_DE  EQU $30A9

STACK_NUM   EQU $33B4

TEST_ZERO   EQU $34E9

KP_SCAN     EQU $3C01

TEST_SCREEN EQU $3C04

CHAR_SET    EQU $3D00

;**************************************************

; =========================

; RESTART ROUTINES - PART 1

; =========================

; RST $10, $18 and $20 call the equivalent subroutines in ROM 1, via RST $28.

;

; RST $00 - Reset the machine.

; RST $08 - Not used. Would have invoked the ZX Interface 1 if fitted.

; RST $10 - Print a character      (equivalent to RST $10 ROM 1).

; RST $18 - Collect a character    (equivalent to RST $18 ROM 1).

; RST $20 - Collect next character (equivalent to RST $20 ROM 1).

; RST $28 - Call routine in ROM 1.

; RST $30 - Not used.

; RST $38 - Not used.

; -----------------------

; RST $00 - Reset Machine

; -----------------------

        ORG $0000

L0000:  DI                ; Ensure interrupts are disabled.

        LD   BC,$692B     ;

L0004:  DEC  BC           ; Delay about 0.2s to allow screen switching mechanism to settle.

        LD   A,B          ;

        OR   C            ;

        JR   NZ,L0004     ; [There is no RST $08. No instruction fetch at $0008 hence ZX Interface 1 will not be paged in from this ROM. Credit: Paul Farrow].

        JP   L00C7        ; to the main reset routine.

L000C:  DB $00, $00     ; [Spare bytes]

        DB $00, $00     ;

; ---------------------------

; RST $10 - Print A Character

; ---------------------------

L0010:  RST  28H          ; Call corresponding routine in ROM 1.

        DEFW PRINT_A_1    ; $0010.

        RET               ;

L0014:  DB $00, $00     ; [Spare bytes]

        DB $00, $00     ;

; -----------------------------

; RST $18 - Collect A Character

; -----------------------------

L0018:  RST  28H          ; Call corresponding routine in ROM 1.

        DEFW GET_CHAR     ; $0018.

        RET               ;

L001C:  DB $00, $00     ; [Spare bytes]

        DB $00, $00     ;

; --------------------------------

; RST $20 - Collect Next Character

; --------------------------------

L0020:  RST  28H          ; Call corresponding routine in ROM 1.

        DEFW NEXT_CHAR    ; $0020.

        RET               ;

L0024:  DB $00, $00     ; [Spare bytes]

        DB $00, $00     ;

; -------------------------------

; RST $28 - Call Routine in ROM 1

; -------------------------------

; RST 28 calls a routine in ROM 1 (or alternatively a routine in RAM while

; ROM 1 is paged in). Call as follows: RST 28 / DEFW address.

L0028:  EX   (SP),HL      ; Get the address after the RST $28 into HL,

                          ; saving HL on the stack.

        PUSH AF           ; Save the AF registers.

        LD   A,(HL)       ; Fetch the first address byte.

        INC  HL           ; Point HL to the byte after

        INC  HL           ; the required address.

        LD   (RETADDR),HL ; $5B5A. Store this in RETADDR.

        DEC  HL           ; (There is no RST $30)

        LD   H,(HL)       ; Fetch the second address byte.

        LD   L,A          ; HL=Subroutine to call.

        POP  AF           ; Restore AF.

        JP   L005C        ; Jump ahead to continue.

L0037:  DB $00          ; [Spare byte]

; ==========================

; MASKABLE INTERRUPT ROUTINE

; ==========================

; This routine preserves the Hl register pair. It then performs the following:

; - Execute the ROM switching code held in RAM to switch to ROM 1.

; - Execute the maskable interrupt routine in ROM 1.

; - Execute the ROM switching code held in RAM to return to ROM 0.

; - Return to address $0048 (ROM 0).

L0038:  PUSH HL           ; Save HL register pair.

        LD   HL,L0048     ; Return address of $0048 (ROM 0).

        PUSH HL           ;

        LD   HL,SWAP      ; $5B00. Address of swap ROM routine held in RAM at $5B00.

        PUSH HL           ;

        LD   HL,L0038     ; Maskable interrupt routine address $0038 (ROM 0).

        PUSH HL           ;

        JP   SWAP         ; $5B00. Switch to other ROM (ROM 1) via routine held in RAM at $5B00.

L0048:  POP  HL           ; Restore the HL register pair.

        RET               ; End of interrupt routine.

; ===============================

; ERROR HANDLER ROUTINES - PART 1

; ===============================

; ------------------

; 128K Error Routine

; ------------------

L004A:  LD   BC,$7FFD     ;

        XOR  A            ; ROM 0, Bank 0, Screen 0, 128K mode.

        DI                ; Ensure interrupts are disabled whilst paging.

        OUT  (C),A        ;

        LD   (BANK_M),A   ; $5B5C. Note the new paging status.

        EI                ; Re-enable interrupts.

        DEC  A            ; A=$FF.

        LD   (IY+$00),A   ; Set ERR_NR to no error ($FF).

        JP   L0321        ; Jump ahead to continue.

; =========================

; RESTART ROUTINES - PART 2

; =========================

; -----------------------------------------

; Call ROM 1 Routine (RST $28 Continuation)

; -----------------------------------------

; Continuation from routine at $0028 (ROM 0).

L005C:  LD   (TARGET),HL  ; $5B58. Save the address in ROM 0 to call.

        LD   HL,YOUNGER   ; $5B14. HL='Return to ROM 0' routine held in RAM.

        EX   (SP),HL      ; Stack HL.

        PUSH HL           ; Save previous stack address.

        LD   HL,(TARGET)  ; $5B58. HL=Retrieve address to call. [There is no NMI code. Credit: Andrew Owen].

        EX   (SP),HL      ; Stack HL.

        JP   SWAP         ; $5B00. Switch to other ROM (ROM 1) and return to address to call.

; ============

; RAM ROUTINES

; ============

; The following code will be copied to locations $5B00 to $5B57, within the old ZX Printer buffer.

; -----------------

; Swap to Other ROM (copied to $5B00)

; -----------------

; Switch to the other ROM from that currently paged in.

; [The switching between the two ROMs invariably enables interrupts, which may not always be desired

; (see the bug at $09CD (ROM 0) in the PLAY command). To overcome this issue would require a rewrite

; of the SWAP routine as follows, but this is larger than the existing routine and so cannot simply be

; used in direct replacement of it. A work-around solution is to poke a JP instruction at the start of

; the SWAP routine in the ZX Printer buffer and direct control to the replacement routine held somewhere

; else in RAM. Credit: Toni Baker, ZX Computing Monthly]

;

; [However, the PLAY commnad bug may be fixed in another manner within the PLAY command itself, in which

; case there is no need to modify the SWAP routine.]

;

; SWAP:

;       PUSH AF           ; Stack AF.

;       PUSH BC           ; Stack BC.

;

;       LD   A,R          ; P/V flag=Interrupt status.

;       PUSH AF           ; Stack interrupt status.

;

;       LD   BC,$7FFD     ; BC=Port number required for paging.

;       LD   A,(BANK_M)   ; A=Current paging configuration.

;       XOR  $10          ; Complement 'ROM' bit.

;       DI                ; Disable interrupts (in case an interrupt occurs between the next two instructions).

;       LD   (BANK_M),A   ; Store revised paging configuration.

;       OUT  (C),A        ; Page ROM.

;

;       POP  AF           ; P/V flag=Former interrupt status.

;       JP   PO,SWAP_EXIT ; Jump if interrupts were previously disabled.

;

;       EI                ; Re-enable interrupts.

;

; SWAP_EXIT:

;       POP BC            ; Restore BC.

;       POP AF            ; Restore AF.

;       RET               ;

;SWAP

L006B:  PUSH AF           ; Save AF and BC.

        PUSH BC           ;

        LD   BC,$7FFD     ;

        LD   A,(BANK_M)   ; $5B5C.

        XOR  $10          ; Select other ROM.

        DI                ; Disable interrupts whilst switching ROMs.

        LD   (BANK_M),A   ; $5B5C.

        OUT  (C),A        ; Switch to the other ROM.

        EI                ;

        POP  BC           ; Restore BC and AF.

        POP  AF           ;

        RET               ;

; ---------------------------

; Return to Other ROM Routine (copied to $5B14)

; ---------------------------

; Switch to the other ROM from that currently paged in

; and then return to the address held in RETADDR.

;YOUNGER

L007F:  CALL SWAP         ; $5B00. Toggle to the other ROM.

        PUSH HL           ;

        LD   HL,(RETADDR) ; $5B5A.

        EX   (SP),HL      ;

        RET               ; Return to the address held in RETADDR.

; ---------------------

; Error Handler Routine (copied to $5B1D)

; ---------------------

; This error handler routine switches back to ROM 0 and then

; executes the routine pointed to by system variable TARGET.

;ONERR

L0088:  DI                ; Ensure interrupts are disabled whilst paging.

        LD   A,(BANK_M)   ; $5B5C. Fetch current paging configuration.

        AND  $EF          ; Select ROM 0.

        LD   (BANK_M),A   ; $5B5C. Save the new configuration

        LD   BC,$7FFD     ;

        OUT  (C),A        ; Switch to ROM 0.

        EI                ;

        JP   L00C3        ; Jump to $00C3 (ROM 0) to continue.

; -------------------------

; 'P' Channel Input Routine (copied to $5B2F)

; -------------------------

; Called when data is read from channel 'P'.

; It causes ROM 0 to be paged in so that the new RS232 routines

; can be accessed.

;PIN

L009A:  LD   HL,L06D8     ; RS232 input routine within ROM 0.

        JR   L00A2        ;

; --------------------------

; 'P' Channel Output Routine (copied to $5B34)

; --------------------------

; Called when data is written to channel 'P'.

; It causes ROM 0 to be paged in so that the new RS232 routines

; can be accessed.

; Entry: A=Byte to send.

;POUT

L009F:  LD   HL,L07CA     ; RS232 output routine within ROM 0.

L00A2:  EX   AF,AF'       ; Save AF registers.

        LD   BC,$7FFD     ;

        LD   A,(BANK_M)   ; $5B5C. Fetch the current paging configuration

        PUSH AF           ; and save it.

        AND  $EF          ; Select ROM 0.

        DI                ; Ensure interrupts are disabled whilst paging.

        LD   (BANK_M),A   ; $5B5C. Store the new paging configuration.

        OUT  (C),A        ; Switch to ROM 0.

        JP   L05E6        ; Jump to the RS232 channel input/output handler routine.

; ------------------------

; 'P' Channel Exit Routine (copied to $5B4A)

; ------------------------

; Used when returning from a channel 'P' read or write operation.

; It causes the original ROM to be paged back in and returns back to

; the calling routine.

;POUT2

L00B5:  EX   AF,AF'       ; Save AF registers. For a read, A holds the byte read and the flags the success status.