THE SYSTEM VARIABLES
OLD ROM SYSTEM VARIABLES NEW ROM SYSTEM VARIABLES
Decimal Hex Name Decimal Hex Name
16384 4000 ERR_NR 16384 4000 ERR_NR
16385 4001 FLAGS 16385 4001 FLAGS
16386 4002 PPC 16386 4002 ERR_SP
16388 4004 E_ADDR 16388 4004 RAMTOP
16390 4006 E_PPC 16390 4006 MODE
16392 4008 VARS 16391 4007 PPC
16394 400A E_LINE 16393 4009 VERSN
16396 400C D_FILE 16394 400A E_PPC
16398 400E DF_EA 16396 400C D_FILE
16400 4010 DF_END 16398 400E DF_CC
16402 4012 DF_SZ 16400 4010 VARS
16403 4013 S_TOP 16402 4012 DEST
16405 4015 X_PTR 16404 4014 E_LINE
16407 4017 OLDPPC 16406 4016 CH_ADD
16409 4019 FLAGX 16408 4018 X_PTR
16410 401A T_ADDR 16410 401A STKBOT
16412 401C SEED 16412 401C STKEND
16414 401E FRAMES 16414 401E BERG
16416 4020 V_ADDR 16415 401F MEM
16418 4022 ACC 16417 4021 SPARE1
16420 4024 S_POSN 16418 4022 DF_SZ
16422 4026 CH_ADD 16419 4023 S_TOP
16421 4025 LAST_K
16423 4027 DB_ST
16424 4028 MARGIN
16425 4029 NXTLIN
16427 402B OLDPPC
16429 402D FLAGX
16430 402E STRLEN
16432 4030 T_ADDR
16434 4032 SEED
16436 4034 FRAMES
16438 4036 COORDS
16440 4038 PR_CC
16441 4039 S_POSN
16443 403B CDFLAG
16444 403C PRBUFF
16477 405D MEMBOT
16507 407B SPARE2
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+-------+-----+-----+----+--------------------------------------------------+ |SYSTEM |OLD |NEW |NO. | | |VARIA- |ROM |ROM |OF | | |BLES |ADDR.|ADDR.|BYT.|PURPOSE | +-------+-----+-----+----+--------------------------------------------------+ |ACC |4022 |- |2 |Value of last expression | |BERG |- |401E |1 |Used by floating point calculator | |CDFLAG |- |403B |1 |Flags relating to FAST/SLOW mode | |CH_ADD |4026 |4016 |2 |Address of the next character to interpret | |COORDS |- |4036 |2 |Coordinates of last point PLOTed | |D_FILE |400C |400C |2 |Address of start of display file | |DB_ST |- |4027 |1 |Debounce status of keyboard | |DEST |- |4012 |2 |Address of variable being assigned | |DF_CC |- |400E |2 |Address of print position within display file | |DF_EA |400E |- |2 |Address of start of lower part of screen | |DF_END |4010 |- |2 |Address of end of display file | |DF_SZ |4012 |4022 |2 |Number of lines in lower part of screen | |E_ADDR |4004 |- |2 |Address of cursor in edit line | |E_LINE |400A |4014 |2 |Address of start of edit line | |E_PPC |4006 |400A |2 |Line number of line with cursor | |ERR_NR |4000 |4000 |1 |Current report code minus one | |ERR_SP |- |4002 |2 |Address of top of GOSUB stack | |FLAGS |4001 |4001 |1 |Various flags | |FLAGX |4019 |402D |1 |Various flags | |FRAMES |401E |4034 |2 |Updated once for every TV frame displayed | |LAST_K |- |4025 |2 |Keyboard scan taken after the last TV frame | |MARGIN |- |4028 |1 |Number of blank lines above or below picture | |MEM |- |401F |2 |Address of start of calculator's memory area | |MEMBOT |- |405D |1E |Area which may be used for calculator memory | |MODE |- |4006 |1 |Current cursor mode | |NXTLIN |- |4029 |2 |Address of next program line to be executed | |OLDPPC |4017 |402B |2 |Line number to which CONT/CONTINUE jumps | |PPC |4002 |4007 |2 |Line number of line being executed | |PR_CC |- |4038 |1 |Address of LPRINT position (high part assumed 40) | |PRBUFF |- |403C |21h |Buffer to store LPRINT output | |RAMTOP |- |4004 |2 |Address of reserved area (not wiped out by NEW) | |S_POSN |4024 |4039 |2 |Coordinates of print position | |S_TOP |4013 |4023 |2 |Line number of line at top of screen | |SEED |401C |4032 |2 |Seed for random number generator | |SPARE1 |- |4021 |1 |One spare byte | |SPARE2 |- |407B |2 |Two spare bytes | |STKBOT |- |401A |2 |Address of calculator stack | |STKEND |- |401C |2 |Address of end of calculator stack | |STRLEN |- |402E |2 |Information concerning assigning of strings | |T_ADDR |401A |4030 |2 |Address of next item in syntax table | |V_ADDR |4020 |- |2 |Address of variable name to be assigned | |VARS |4008 |4010 |2 |Address of start of variables area | |VERSN |- |4009 |1 |First system variable to be SAVEd | |X_PTR |4015 |4018 |2 |Address of char. preceding syntax error marker | +-------+-----+-----+----+--------------------------------------------------+ |
[Thunor: Note that the book simply includes a list of addresses, and so I have decided to implement a diagram that presents the addresses in a more informative way.]
OLD ROM NEW ROM
Top of memory --+------------------+ +------------------+-- Top of memory
| | | Reserved area |
| | +------------------+-- (RAMTOP)
| | | GOSUB stack |
| | +------------------+-- (ERR_SP)
| | | Machine stack |
| | +------------------+-- SP
| Machine stack | | Spare memory |
SP --+------------------+ +------------------+-- (STKEND)
| Spare memory | ^ | Calculator stack |
(DF_END) --+------------------+ | +------------------+-- (STKBOT)
| Screen | | | Edit line |
(D_FILE) --+------------------+ +------------------+-- (E_LINE)
| Edit line | | User variables |
(E_LINE) --+------------------+ +------------------+-- (VARS)
| User variables | | Screen |
(VARS) --+------------------+ +------------------+-- (D_FILE)
| User program | | User program |
4028h (16424d) --+------------------+ +------------------+-- 407Dh (16509d)
| System variables | | System variables |
4000h (16384d) --+------------------+ +------------------+-- 4000h (16384d)
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