PRINTING A SYMBOL TABLE FOR THE AIM-65 ASSEMBLER

Richard F. Olivia
Biological Sciences, Smith College
Northampton, MA 01063

The assembler for Rockwell's AIM 65 makes assembly-language programming very convenient, particularly in conjunction with the excellent editor that is part of AIM 65's monitor. However, the assembler does not include an option to print the symbol table, although it does create such a table in memory. The following program is one way of decoding and printing the symbol table. In revising a program, a print-out of the symbol table can be very helpful.

On entering the AIM 65 assembler from the monitor, you are asked for the addresses that start and end the symbol table. The assembler places your answers in zero-page addresses 3A, 3B ("FROM") and 3E, 3F ("TO"). After assembly, the total number of symbols is available in addresses OB, OC (in high, low order). The symbol table itself consists of sequential eight-byte entries. The first six bytes of each entry are the symbol name, in ASCII characters (the assembler enters spaces if the symbol is less than six characters), and the last two bytes are the symbol's address, in hex notation.

The program to print the table reads through the table using indirect addressing indexed by Y. It establishes the variable ADDR (at locations 00 and 01), which provides the address of the first character of the current symbol. ADDR is initially set equal to the address in "FROM (3A, 3B); it is incremented by eight after each symbol is printed. For each symbol, the Y register is incremented from zero to seven to access the successive bytes of that symbol.

A second variable, COUNT (addresses 02 and 03), keeps track of the number of symbols that remained to be printed. COUNT is initially set equal to one less than the total number of symbols (from addresses 0B and 0C), and it is decremented by one after each symbol is printed. After COUNT reaches zero (the last symbol is numbered zero, which is why the initial count is one less than the total), the program exits and prints the total number of symbols in hex notation. The program uses AIM monitor subroutines to print the ASCII and hex characters. It also turns the AIM printer on and off at the start and end of the table, which I find very handy.

The listing given below places the program at locations 0200-027D, which are available on every AIM 65. The program could of course be placed in other memory locations, and it would be very convenient in a PROM. At the end of the listing, the program was run to list its own symbol table.