bammi@cwruecmp.UUCP (Jwahar R. Bammi) (02/14/86)
We finally got some ROMS and we had four machines that we had upgraded to 1 Meg. Here is a set of experiences that may help some people that may run in the same problems that we did. All the machines were running fine with the upgrade and without the resistors. I put all 6 68 O (O == ohms) resistors in, and it worked fine with the Roms and all. Now we went to do my office mate's machine. We put the 68 O resistors, no roms and the machine recognized the upper 512K, but we started getting random errors (looked like the rams we not holding data). So we took one resistor out of the pin 4 (RAS) bus of the upper 512K and hooked the bus directly to the MM chip. Worked fine (the 68 O resistors were in on the 2 pin 15 (CAS) busses of the upper 512K). The lower 512 K was doing just fine with all the resistors in. The only difference between between this machine and mine was that I had Hitachi chips and this machine had Oki chips. So we guessed that they had different operating points, and so we tried a lower value resistor, 39 O on the pin 4 (RAS) bus. This time we started getting consistent errors (every alternate address above 512K read FE instead of FF). So we went for a even lower value resistor, 27 O, and then everything worked out just fine. Now we have the Rom in, and its doing just fine. Has anyone else come across such problems?? We mounted our resistors on a little piece of PCB and stuck it to the left of the Rams, and ran wires from the MM chip to the appropriate spots (after cutting the 3 lines ( RAS and the two CAS's of the lower 512K), instead of soldering the resistors to the traces or the memory chip directly. -- Jwahar R. Bammi Usenet: .....!decvax!cwruecmp!bammi CSnet: bammi@case Arpa: bammi%case@csnet-relay CompuServe: 71515,155