Lack of robustness with 1K and 4K RAM chips (was Re: 2116 and other old memory chips)

--- Tony Duell <ard(a)p850ug1.demon.co.uk> wrote: I, too, have had these fail numerous times. Much more so than other SRAMs or any DRAMs. The only ones that came close were from the same era: 4096 DRAMs - I have them on some LSI-11 boards and inside a Z-80-based Gorf. When I first got all the parts together to refurb a full-sized Gorf machine, the internal tests showed a memory fault on one of the DRAM boards, covered in 4096 chips. I use the LSI-11 CPU, a COMBOARD (for its memory mapping/DMA engine) and a Fluke tester to check the 4K DRAMs - plug the COMBOARD on the Qbus, put the test RAMs on the LSI-11 board, plug the Fluke emulator/tester in the 68000 socket on the COMBOARD, fire it all up, hit the DMA enable bit on the COMBOARD, then through the Fluke, test a range of 68K memory that corresponds to the appropriate range of Qbus memory addresses and voila - a 4096 tester with about $25K-new-cost worth of test gear. (The Qbus COMBOARD memory map is divided into 4 regions, RAM, shared-memory, I/O and ROM. There are 22 bits of 68K space available to map each and every Qbus location into some valid local address. Who needs mapping registers! No FUBAR on a Qbus!) The first COMBOARD used 2114 SRAMs because they were more reliable than Intel's DRAMs of the day (plus the XC68000 would occasionally enter a microcode fault and reset, causing Z-80-style bus-driven refresh mechanisms to pause too long, letting all the bits leak out). -ethan ===== Visit "The Seventh Continent" http://penguincentral.com/penguincentral.html __________________________________________________ Do You Yahoo!? Get personalized email addresses from Yahoo! Mail http://personal.mail.yahoo.com/