--- Tony Duell <ard_at_p850ug1.demon.co.uk> wrote:
> The 2114 SRAM is single-supply rail (+5V only). Again, it was made by
> several companies (but I think most of the time it was called the 2114).
> It also happens to be the chip I've had the most failures from :-)
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
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Received on Fri Jul 06 2001 - 20:38:22 BST