A project log for z80ctrl

AVR-based bootloader and IO card for RC2014 retrocomputer

jb-langstonJ.B. Langston 01/02/2019 at 00:210 Comments

I've gotten MSX-BASIC to run on the RC2014 with my TMS9918A video card and my z80ctrl card emulating the MSX keyboard.

I have checked the keyboard emulation code into GitHub.  It takes ASCII characters from the z80ctrl UART and converts them into MSX keyboard scan codes using a table.  Currently it doesn't support some of the control keys on the MSX keyboard such as stop and the arrow keys.  I will keep working on this, but it's usable as is.

The MSX-BASIC ROM can be obtained from the blueMSX emulator.  Copy MSX.rom from the Machines\Shared Roms directory of your blueMSX installation to your z80ctrl SD card. Once you've copied it, load and run it from z80ctrl:

z80ctrl>clkdiv 5
z80ctrl>loadbin 0 msx.rom
z80ctrl>run 0

One of the nice things about MSX-BASIC is that it has built-in graphics primitives for the TMS9918A video card, unlike, say, MBASIC on CP/M.  I have used these primitives to draw an analog clock using the time pulled from the RTC chip on my z80ctrl IO expander, which is shown in the video. The BASIC source code is available on GitHub.

Currently, there is no support for MSX tape or disk drives, so you can't save your program once you have typed it in. The way I worked around this was to edit the program on my PC and then paste it into TeraTerm.  I had to set a 50 ms per-character delay in order to get the program to reliably type in when pasted.  A faster brute force method of saving your program once you have typed it in is to press the halt button on the z80ctrl and run 

z80ctrl>savebin 8000 ffff image.bin 

This will save the complete state of your BASIC interpreter so that you can load it back up the next time using and pick up where you left off.  Next time, to pick up where you left off, run

z80ctrl>loadbin 0 msx.rom
z80ctrl>run 0
*press the halt button*
z80ctrl>loadbin 8000 image.bin

Your program should now be in exactly the same state as it was before. You can list it to verify it is there, then run it.

Here are some good references I have found for MSX-BASIC.