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interpreter_20internal_20variables

Interpreter internal variables

by Richard Russell, June 2009

The table below lists the addresses and purposes of a number of memory locations used internally by the BBC BASIC for Windows interpreter. Only very rarely will a BASIC programmer be interested in these values, and only experienced programmers with a good understanding of the inner workings of the interpreter should attempt to use them. It will hardly ever be required to write to these locations, and doing so without a full understanding of the consequences is likely to crash the interpreter or make it unstable.

The addresses shown in the first column are appropriate when accessed directly from BASIC, but they cannot be used from assembler code. In the latter case the locations must be accessed indirectly, for example instead of !408 use [^!408].

Address
Purpose
!108
Base pointer to linked list of variables etc. starting with A
!112
Base pointer to linked list of variables etc. starting with B
!116
Base pointer to linked list of variables etc. starting with C
!120
Base pointer to linked list of variables etc. starting with D
!124
Base pointer to linked list of variables etc. starting with E
!128
Base pointer to linked list of variables etc. starting with F
!132
Base pointer to linked list of variables etc. starting with G
!136
Base pointer to linked list of variables etc. starting with H
!140
Base pointer to linked list of variables etc. starting with I
!144
Base pointer to linked list of variables etc. starting with J
!148
Base pointer to linked list of variables etc. starting with K
!152
Base pointer to linked list of variables etc. starting with L
!156
Base pointer to linked list of variables etc. starting with M
!160
Base pointer to linked list of variables etc. starting with N
!164
Base pointer to linked list of variables etc. starting with O
!168
Base pointer to linked list of variables etc. starting with P
!172
Base pointer to linked list of variables etc. starting with Q
!176
Base pointer to linked list of variables etc. starting with R
!180
Base pointer to linked list of variables etc. starting with S
!184
Base pointer to linked list of variables etc. starting with T
!188
Base pointer to linked list of variables etc. starting with U
!192
Base pointer to linked list of variables etc. starting with V
!196
Base pointer to linked list of variables etc. starting with W
!200
Base pointer to linked list of variables etc. starting with X
!204
Base pointer to linked list of variables etc. starting with Y
!208
Base pointer to linked list of variables etc. starting with Z
!212
Base pointer to linked list of variables etc. starting with _
!216
Base pointer to linked list of variables etc. starting with `
!220
Base pointer to linked list of variables etc. starting with a
!224
Base pointer to linked list of variables etc. starting with b
!228
Base pointer to linked list of variables etc. starting with c
!232
Base pointer to linked list of variables etc. starting with d
!236
Base pointer to linked list of variables etc. starting with e
!240
Base pointer to linked list of variables etc. starting with f
!244
Base pointer to linked list of variables etc. starting with g
!248
Base pointer to linked list of variables etc. starting with h
!252
Base pointer to linked list of variables etc. starting with i
!256
Base pointer to linked list of variables etc. starting with j
!260
Base pointer to linked list of variables etc. starting with k
!264
Base pointer to linked list of variables etc. starting with l
!268
Base pointer to linked list of variables etc. starting with m
!272
Base pointer to linked list of variables etc. starting with n
!276
Base pointer to linked list of variables etc. starting with o
!280
Base pointer to linked list of variables etc. starting with p
!284
Base pointer to linked list of variables etc. starting with q
!288
Base pointer to linked list of variables etc. starting with r
!292
Base pointer to linked list of variables etc. starting with s
!296
Base pointer to linked list of variables etc. starting with t
!300
Base pointer to linked list of variables etc. starting with u
!304
Base pointer to linked list of variables etc. starting with v
!308
Base pointer to linked list of variables etc. starting with w
!312
Base pointer to linked list of variables etc. starting with x
!316
Base pointer to linked list of variables etc. starting with y
!320
Base pointer to linked list of variables etc. starting with z
!324
Base pointer to linked list of functions (FN)
!328
Base pointer to linked list of procedures (PROC)
!332
Pointer to string accumulator (65536 bytes)
!336
Pointer to string input and temporary buffer (256 bytes)
!340
Current value of PAGE
!344
Current TRACE setting
!348
Current value of LOMEM
!352
Pointer to start of heap free space (END)
!356
Current value of HIMEM
!360
Pointer to first installed LIBRARY (if any)
!364
Pointer to NUL-terminated error string (REPORT$)
!368
Temporary storage for ON ERROR LOCAL
!372
Pointer to current ON ERROR statement (if any)
!376
Current DATA pointer (if any)
!380
Current value of COUNT
!384
Pointer to (or within) currently-executing statement
!388
Pointer to current ON TIME statement (if any)
!392
Pointer to current ON CLOSE statement (if any)
!396
Pointer to current ON MOVE statement (if any)
!400
Pointer to current ON SYS statement (if any)
!404
Pointer to current ON MOUSE statement (if any)
!408
Address at which the most recent error was detected (used to find ERL)
!412
Current 'random' number, bits 0-31 (RND)
?416
Current 'random' number, bit 32 (0 or 1)
?417
Current value of WIDTH
?418
Current value of ERR
?419
Current *FLOAT (bits 0,1) *HEX (bit 2) *LOWERCASE (bit 3) and OPT (bits 4-7) setting


!420
Pointer to temporary path/filename buffer (256 bytes)
!424
Pointer to *KEY string storage (256 bytes)
!428
Pointer to keyboard queue (256 bytes)
!432
Pointer to event queue (512 bytes)
!436
Pointer to current *KEY string expansion
!440
Pointer to user-defined character storage (2048 bytes)
?444
Current 'cursor movement control' setting (VDU 23,16,…)
?445
Scroll flag (used by Copy Key emulation)
?446
Current *INPUT (bits 4-7) and *OUTPUT (bits 0-3) setting


!536
*SPOOL/*SPOOLON channel number
!540
*EXEC channel number
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interpreter_20internal_20variables.txt · Last modified: 2018/03/31 13:19 (external edit)