Need to programme the Mega to access the SRAM, directly.

[rhshorts]

Z80 uses BUSREQ and BUSACK lines to manage DMA. Both are active low. Device, requesting DMA access:

1. puts BUSREQ low;
2. waits for Z80 to put BUSACK low;
3. Access SRAM directly via Address Bus, Data Bus, MREQ and RD or WR
4. and, finally, puts BUSREQ low.