The Microcontroller Idea Book - Jan Axelson's Lakeview Research

Chapter 13
Listing 13-1. Source file for a simple program to test assembly-language
interfacing with BASIC-52.
org 3000h ;location where program will
;load in RAM
cpl p1.0 ;complement Port 1, bit 0
;(pin 1)
ret
;return to BASIC-52
end
specifies 3000h. You can change the address to match whatever locations you have available
in your system.
The program body’s single instruction complements bit 0 of Port 1, changing it from high
to low or low to high. A ret instruction then returns control to BASIC-52.
To create and test the routine, do the following:
Use a text editor to create a file containing Listing 13-1.
Use your assembler to assemble the file. A typical command line looks like this:
A51 bittog.asm -L bittog.lst -O bittog.hex
The above command tells the assembler to create two files: the listing file bittog.lst (shown
in Listing 13-2) and the object file bittog.hex, in Intel hex format (shown in Listing 13-3).
File Formats for Assembly-language Routines
This is a good time to look at Intel Hex and other file formats in greater detail. Most EPROM
programmers are able to program EPROMs directly from the files created by assemblers
and compilers, but the file must be in a format that the programmer recognizes. Three
Listing 13-2. Listing file created by assembling the source file in Listing 13-1.
3000 org 3000h ;location where program will
;load in RAM
3000 b2 90 cpl p1.0 ;complement Port 1, bit 0
;(pin 1)
3002 22 ret ;return to BASIC-52
222 The Microcontroller Idea Book