You should have “Hello World.asm” open in ConTEXT from the Setting it up stage. Let’s see what it does.

WLA DX banking setup

In the Memory section we learned about the Z80 memory map. If we want to use more than 48KB of ROM then we need to tell WLA DX all about the slots; however, for a simple case (as in this one) all we need to do is tell it where and how big the ROM is.

; WLA-DX banking setup
defaultslot 0
slotsize $8000
slot 0 $0000

bankstotal 1
banksize $8000
banks 1

I put a huge comment there to remind me what it is for and to “split up” the file with the horizontal lines. This is just a matter of taste.

The directives basically say we want one 32KB ($8000 bytes) “bank” of ROM and that it starts at address $0000 in the memory map (slot 0).

SDSC tag

; SDSC tag and SMS rom header
.sdsctag 1.10,"Hello World!","SMS programming tutorial program (bugfixed)","Maxim"

This is one of the niceties that you ought to add to your homebrew software. Kindly added to WLA DX after being invented on the SMS Power development forum, it allows you to embed useful information about your program - its name, version, date, author and notes - into the resulting ROM image. It’s another WLA directive - you write the version, name, notes and author name and it fills in the date for you.

By adding this tag you will also prompt WLA to insert a valid SMS rom header. This is something found in (almost) all SMS roms which acts to verify that the cartridge is correct when played on an original system. It’s not absolutely necessary, but you do want your program to work on a real SMS, don’t you?

You can add this anywhere in your source. Putting it at the start reminds you that it’s there and that you ought to update it, though.

Where to put the code

.bank 0 slot 0
.org $0000

This tells WLA DX that code (and data) that we are about to specify should go in ROM bank 0 (even though there is only one ROM bank) and that this bank will be in slot 0 (even though there is only one slot). Then we say that we want the code to start right at the beginning (location $0000).

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