Recently I found z88dk, “the C and assembler development kit that comes ready out-of-the-box to create programs for over 100 z80-family (8080, 8085, gbz80, z80, z180, ez80_z80, KC160, Rabbit 2000, 3000, 4000, 5000) machines”. Given that z88dk can create binaries for AgonLight computer which I have now (albeit only in Z80 mode with 64k of memory accessible), I naturally got interested.

First attempt

Let us take the following assembler file zfirst.asm:

CHPUT equ 00A2h

        ld      a,'A'
        call    CHPUT

Compiling it with zcc +msx -subtype=rom2 -o zfirst.rom zfirst.asm yields an error about undefined symbol _main. Of course, z88dk links the executable with crt0 which expects (as it would happen with C program) that the entry point _main is defined.

So, given my interest in retrocomputing, I have bought myself Agon Light computer, AgonLight2 version.

What is it?

It is actually modern “old” computer, having 512 kilobytes of memory and eZ80 CPU. The CPU has two modes:

• one is fully compatible with classic Z80 CPU (8-bit, 64 kilobytes of addressable RAM)
• one is slight extension of it (24-bit, and this is not a typo)

There is also ESP chip which handles keyboard, graphics, and audio.

This is the next installment in my MSX Assembly 101 series. We are going to develop here printd routine, which will print the decimal value of the byte is the accumulator.

Comparing to printh (hexadecimal representation) there is an additional complication: hexadecimal representation always contains two digits (for example, the byte 0x01 is printed as 01, with leading zero); the number of digits in the decimal representation depends on the value of the number: