+
When a programmer writes an assembly language program instead of directly referring to a memory address over and over again they use a symbolic name instead. For example, instead of always directly hard-coding $C000 everywhere to read the keyboard they would instead write: -
- KEYBOARD EQU $C000
-1 LDA KEYBOARD
- BPL 1
+
+ ORG $300
+ KEYBOARD EQU $C000
+300:AD 00 C0 .1 LDA KEYBOARD
+303:10 FB BPL .1
+305:8D 00 04 STA $0400
+306:60 RTS
+ Let's try this out in the debugger. Make sure AppleWin is running. Press F2 (to reboot), then Ctrl-F2 (to break), and F7 (to enter the debugger.) + If you don't want to type in the following hex code, you can select it, copy it (Ctrl-C), and paste it into the Debugger console (Ctrl-V). +
+
+300:AD 00 C0 10 FB 8D 00 04 60
+300L
+
+ Press F7 to exit the debugger, then type: +
+
+HOME:CALL 768
+
+ Press Enter. The emulated computer will wait for your to press a key and then echo it in the top left. +
++ When debugging assembly programs since you typically don't have the source file availabe you can tell the debugger how to interpret a memory address as a variable name or symbol. + A symbol is the symbolic name and the address assigned to it. +
AppleWin supports loading of the assemblers ACME, and Merlin's symbol tables -- a collection of symbols, one per line, organized and collectively called a symbol table. The semi-colon is a comment-till-end-of-line. The file format per line is: ADDRESS SYMBOL
-e.g. -
e.g. There are 9 symbol tables to help organize "modules"; each symbol table individually can be turned off/on independently.
+
+ There are 9 symbol tables to help organize "modules"; each symbol table individually can be turned off/on independently.
+
; IO Map
C000 KEYBOARD
MAIN APPLE2E.SYM
BASIC A2_BASIC.SYM
@@ -37,11 +60,11 @@ C000 KEYBOARD
PRODOS A2_PRODOS.SYM
On startup the debugger reads 3 symbol tables by default: Main, Basic, User1.
- +Looking up symbols is easy. If you can't remember an address of a symbol, or the reversse -- can't remember the symbol for an address -- you can use the following symbol commands: - (#### referes to either a hex address or a symbolic name) -
+ (#### referes to either a hex address or a symbolic name) +
SYM
+SYM
Display
+ Display
the number of symbols in the Main, User, and Source symbol tables.
SYM
+ SYM
LIFE = 300
E
+ E
LIFE 64