Reply 20 of 22, by Moogle!
Horun wrote on 2020-08-19, 22:52:Moogle! wrote on 2020-08-19, 18:25:
Minor update. Got the DS1000 up off the board, but I somehow managed to break three of its legs off. Got a socket down and tried a compatible chip from another board (one of those bigger, blockier types) with 40NS delay. It tries to boot with that, but it's gets stuck with 0A on the POST card. I then went and found another one (again, another big blocky one) that was also 50NS like the original Dallas chip, and it does boot with that. Neither works at 33Mhz though.
I think you need to slow/add-wait time, not speed up/reduce. The DS1000-40 is roughly 20% less wait time by TAP5 than DS1000-50. By increasing from 25Mhz to 33 you are increasing speed by 30%. If you could find a DS1000-60 or -75 it would nearly balance that speed increase by adding more wait time. One thing: all of the Dallas DS1000 -20 thru -100 still have 2nS as nominal delay on Taps 1 and 2. So if some critical part was clocked/signaled off Tap1 or Tap2 any of those could be getting signals too quickly no matter which DS1000 you used at 33Mhz. Think of it like a typical VLB controller and you increase board clock to 40Mhz from 33Mhz, you need to add wait states either on board to VLB if it has them or on the VLB card itself (thru jumpers). Yes am simplifying things but going to a DS-40 is going wrong direction.
I have been wondering on this as well, and indeed, the 40NS delay chip came from an old 386. But the other 50NS delay chip that I got came from a 286. It's all too confusing. D: