Symbols

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

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. 

; IO Map
C000 KEYBOARD

There are 9 symbol tables to help organize "modules"; each symbol table individually can be turned off/on independently. 

 MAIN    APPLE2E.SYM
 BASIC   A2_BASIC.SYM
 ASM     A2_ASM.SYM
 User1   A2_USER1.SYM
 User2   A2_USER2.SYM
 Src1    A2_SRC1.SYM
 Src2    A2_SRC2.SYM
 DOS33   A2_DOS33.SYM
 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)



Command

Effect

SYM

Display the number of symbols in the Main, User, and Source symbol tables.

SYM ####

Look-up the Symbol or Address, and display which Symbol Table it is in.

SYMUSER LOAD

Reloads the User Symbol Table: A2_USER1.SYM

SYMUSER CLEAR

Clears the User Symbol Table from RAM.

SYMMAIN ####

Look-up only in the Main symbol table.

SYMUSER ####

Look-up only in the User symbol table.

SYMSRC ####

Look-up only in the Source symbol table.

SYM name = ####

Add (or update) a symbol in the User table with the new Address.

SYM ! name

Remove a symbol from the User table.

E symbol ##

Set memory (at the symbol Address) to the 8-Bit (byte) Value.

EB symbol ####

Alias for E.

E8 symbol ####

Alias for E.

EW symbol ####

Set memory (at the symbol Address) to the 16-Bit (word) Value.

E16 symbol ####

Alias for EW.



Examples:

Input

Effect

SYM

Displays number of symbols in the Main, User, and Source tables.

SYMMAIN CLEAR

Clears the main symbol table!!

SYMMAIN LOAD APPLE2E.SYM

Reloads the main symbol table.

SYM FA62

Look up the Address $FA62 (RESET).

SYM HOME

Look up the Address $FC58 (HOME).

SYM LIFE = 300

Define a new user symbol, called “Life” at Address $0300.

E LIFE 64

Set 8-Bit variable (@ $0300)“Life” to 100 (decimal).

ew life 3e8

Set 16-Bit variable (@ $0300)“Life” to 1000 (decimal).