demik
Well-known member
Easier to just go for 4 layersAlso the cost of the PCB is sort of dwarfed by the cost of assembly and parts. One of the argument in favor of a resistor ladder for VGA is the 12.50€ list price (quantity of 1) at Mouser for the DAC chip... I didn't realize until I added it how expensive analog chips are. The CPLD is only 2.70€ if you get the fastest one (probably not needed, but not much more expensive than the slowest).
XC7A35 on the FPGA board I have, though they are available with the 50/75/100 as well. But a 35 is more than enough unless adding an heavy-duty crypto engine and/or a lot of acceleration to the framebuffer (even a 35 fit my custom VexRiscv core for the SBusFPGA's cg6 easily, if the crypto core is not present).
The 'fan' header is sort of just-in-case; some SPARCstation have borderline cooling (the 10 is famous for its overheating issue when fully kitted, the quad-CPU version was announced but never delivered because of that), and the stacked design of the SBusFPGA blocks airflow so I added a 5V fan header ; I figure it could be useful in a Mac as well. It could also be used if some NuBus signals needs a missing pull-up/down. The 3.3V/GND header is also there for emergency pull-up/down. I should also add some testing points to make using a logic analyzer easier, but I'm not sure where / how - and the 2.54" header to the FPGA board does give some reasonable level of accesses to its signals; ditto the large NuBus DIN connector.
... now that you've mentioned the fan, makes me think I should check how much power the 12V line offers, a 12V fan header could be useful as well (the 12V line on SBus is very limited in power). There's room on that board, might as well take advantage of it![]()
Indeed. The DIP-44 was kinda a joke
As for looking at NuBus signals, you can use the slot next to your board for emergency, besides the IRQ one, all pins should be common IIRC.