Reply 120 of 291, by mkarcher
kdr wrote on 2020-10-17, 11:43:But in the case of the ERGO480 and SPEGASYNC cards, it's absolutely the RAM speed that prevents the card from working at 10Mhz. The SPEGASYNC has 120ns RAM and only works reliably at 8Mhz, while the ERGO480 has 100ns RAM and it works reliably at 10Mhz. I even did some crazy stuff like swapping the EGA chips and the custom gate array between the two cards, since they're nominally the same chips on both cards. (The RAM, alas, is not socketed.) While I agree that the ISA bus speed *shouldn't* have an effect, given that the sequencer which controls the video RAM timing is clocked by the video dot clock, some aspect of the memory read/write timing is influenced by what speed the ISA bus is running at.
Wait a second - the ERGO480 does not just have faster RAM, it also has a faster dot clock. The SPEGASYNC runs at 14.318/16.267MHz, and the ERGO480 runs at 28.5/32.0. So the memory access is way faster on the ERGO480, because the sequencer is clocked at approximately twice the speed. Did you already try swapping the crystals to detect whether the dot clock or the RAM speed is the significant difference?
