EMMA 02

General Information

The COMIX-35 is an open-source clone of the COMX-35 home computer. 

The COMIX is very similar to the COMX with the main difference being that the COMIX uses SRAM instead of DRAM. The advantage here is that SRAM doesn't need any 'refresh' like is done for the DRAM in the COMX. The DRAM refresh on the COMX is done via DMA out instructions so not having these on the COMIX means it runs quite a bit faster than the COMX. 

Small disadvantage of not having the DRAM refresh is that some existing software is depending on the DRAM refresh. DMA out is done with R0 and causes R0 to increment constantly. Some sofwtare uses R0 as a random generator or uses it as input to random generator routines. One example is Space Invaders which without DRAM refresh will not run correctly (enemies will not fire bullits). To overcome this problem I have created a small fix in the COMX rom file to do one LDA R0 during the interrupt routine. This is a lot less frequent compared to the DRAM refresh DMA out but will result in a somehwat better random generator handling. 

Technical specifications

Clock: 2.813 (PAL) or 2.835 MHz (NTSC)
Memory:
      32 KB RAM and 3 KB Video RAM
      16 KB ROM
Video: CDP1869/CDP1870
Sound: CDP1869
Keyboard: CDP1871

Links

GitHub page for the COMIX.