I thought this was about the VIC badlines inhibiting faster serial comms due to a bug in the serial chip. It's fuzzy, but some things in the C64 are bit banged

I thought this was about the VIC badlines inhibiting faster serial comms due to a bug in the serial chip. It's fuzzy, but some things in the C64 are bit banged, and the badlines necessary for video DMA make that difficult at higher speeds.