Hardware vs Simh (and FPGA)

On Apr 27, 2013, at 20:02, Sytse van Slooten <sytse at sytse.net> wrote: The DE1, at least, has series resistors on the 40-pin external headers so that you can interface directly to 5v. The ESD protection diodes on the inputs limit the voltage applied to the actual input transistors to acceptable levels, and the series resistors limit the current flowing through the diodes so they don't burn up. I don't recall offhand whether the DE0 did the same thing, but the schematic is available. Don't forget that a 3.3v output will work fine with 5v TTL inputs as well. The interface isn't necessarily suited for hooking direct to a big bus, though; you'd probably want to pass through a stronger driver transceiver first. I should point out that those headers aren't suited for plugging directly into an IDE drive; the power and ground pins land on some meaningful data pins. You need to make an adaptor. Also, avoid using 80-conductor cables with those connectors; those cables internally bus the IDE grounds together, which don't correspond to the grounds on the board. You won't short power to ground or anything like that, but you will lose a few otherwise useful pins. On the bright side, the DE0 and DE1 use the same pinouts for those connectors, so things should be cross-compatible. The DE0 even runs some clock pins out there, which can be pretty useful. - Dave