Tube Time

Can't correctly write mac400 with Greaseweazle

9

Writing 400K single sided disks using a Greaseweazle (firmware 1.1) appears to be partially broken. The resulting disks can be read in 800K drives but not in 400K drives.

MDA 70Hz RAM issues

3

MDA (70Hz VGA compatible) on some boards has issues with the attribute byte getting corrupted by the previously-read character byte. This shows up as spurious underlines, inverse video, etc on...

These all appear to be timing issues. Investigate the relationship between the display enable/vsync bits in the status register and the sequencer.

The arbitration logic between the SRAM, the CGA pixel engine, and the ISA bus isn't quite intelligent enough and triggers a lot of CGA snow--more than the original card.