Alex Freed wrote:
Steven Hirsch wrote:DIP package PROMs. When my eBay purchased Advin Pilot 143 programmer arrived, I read the PROMs and, unless the programmer is defective, all of them are programmed as a chip full of 0fh values. This is not correct and would explain the misbehavior.My money is on the defective programmer. Can't imagine how the chips can get to this state if they were ever good.
No, I've checked several other types of bipolar proms and the programmer is just fine. The PROMs with my DDT boards were likely programmed from the incorrect image or buffer. Since they are 4-bit devices, the buffer was probably just a block of 0ffh (that reads as 0fh from the device since there are no pullups on the top 4 data bits). The proper binary image for the PROMs is available and was sent with the kit. It is about 98% 0ffh, with a few different 0xh values here and there.
It's also the only thing that makes sense to explain the symptoms. NMI is not being vectored into the DDT firmware when the magic break button is pushed. One of the 74S287 chips is responsible for a portion of the logic that makes this happen. I've replaced every non-programmable chip on the board, checked all sockets point-to-point with an ohmmeter and verified the EPROM and PAL programming. All that's left are the PROMs, which appear to have the incorrect image.