a80 1.4.1

a80

a80 is an assembler written in D for the Intel 8080 (and, by extension, the Zilog Z80) CPU. It produces binaries for CP/M using the standard entry point of 0x100.

a80 is developed on OpenBSD but should work on any system that D targets.

a80 is not an exact clone of any pre-existing CP/M assember, nor does it want to be. The differences will be explained in this document.

a80 also is quite conscious about its design practice and implementation. It is written to be the subject of a series of blog posts in which we attempt to demystify the building of programming tools, and as such very intentionally does not use some very obvious data structures. And it may make some seemingly peculiar design choices. My goal is to have written a real assembler for a real CPU that you can still purchase today (in the form of the Z80) that true beginners can come to understand.

After the blog series, if we want to turn this into a clone of an existing CP/M assembler, I'm all for it.

Bug reports are welcome at any time.

Usage

a80 file.asm

The output will be file.com.

Syntax

A line of assembly takes the following form:

[label:]	[op	[arg1[, arg2]]]	[; comment]

An example of an assembly program can be found in fib.asm.

a80 only understands Intel 8080 opcodes.

The CP/M EQU directive is supported but in a slightly altered syntax. It must be in the form:

label:	equ	<value>

Where value must be a number. You cannot use other labels as a value nor can you use expressions.

All op and arg must be lowercase, though labels may include capital letters.

Numbers

All numbers must be in hex and must end with an h. If a hex number begins with a-f, it must be prefixed with 0. This is not too dissimilar from other CP/M assemblers.

Strings

The DB pseudo-op is available. Strings can be written within single quotes. Single characters will be interpreted to ASCII.

Note this important distinction: db 0 will output '0' or 0x30 in ASCII. db 0h will output 0x00.

If you want a comma you need to use db 2c or put it in a string.

License

ISC license. See LICENSE for more information.