mark@mips.com (Mark G. Johnson) (03/31/91)
In article <7905@uceng.UC.EDU> lbechtle@uceng.UC.EDU (laurie bechtler) writes: >a shmoo plot is just a graphical representation of some kind >of circuit condition versus two input variables. Pick >an output criterion, say, does the circuit pass some specific functional >test? Place an X everywhere on the plot that the circuit passes the >test. You end up with some funny blob shape full of X's that shows >you where (on that particular set of axes) the circuit functions. And the classic shmoo (often printed as "schmoo") plot is supply voltage on the X axis, access time (or clock frequency) on the Y axis. For example, ACCESS TIME "X" = PASS (ns) 15.0 + XXX 14.0 | XXXX 13.0 | XXXX 12.0 | XXXXXX 11.0 | XXXXXXXX 10.0 + XXXXXXXXXXXX 9.0 | XXXXXXXXXXXXXXXXXXX 8.0 | XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX 7.0 | XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX 6.0 | XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX 5.0 + XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX 4.0 | XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX 3.0 | XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX 2.0 | XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX 1.0 | XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX 0.0 | XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX -------+--------+--------+--------+--------+--------+--------+-- VDD 3.0v 3.5v 4.0v 4.5v 5.0v 5.5v 6.0v (volts) This device (a memory chip) slows down dramatically as the supply voltage is reduced. At 5.5v it's a 6.0 nanosecond chip, but at 4.5v it's 8ns. "Shmoo" is derived from a character in the Lil Abner comic strip and not from "mho" the units of inverse resistance (conductance). -- -- Mark Johnson MIPS Computer Systems, 930 E. Arques M/S 2-02, Sunnyvale, CA 94086 (408) 524-8308 mark@mips.com {or ...!decwrl!mips!mark}
wbrown@beva.bev.lbl.gov (Bill Brown) (04/11/91)
'Way back in the olden days, when computers were built out of REAL
transistors and resistors and capacitors and stuff instead of all those
little bug-looking IC things, there was something called "core Memory"
which consisted of little ferritte (sp?) donuts strung on wires.
Several wires ran thru each donut, x-drive, ydrive, inhibit drive, and
read. One computer I used to help babysit had really flakey memories.
In an attempt to keep it working, every week we had to mess with the
memory drive currents. This usually consisted of tweaking the x & y drive
currents and observing where we started to pick up or drop bits. These
points were recorded on a piece of graph paper. When we got done the picture
really did look a lot like a schmoo. We then eyballed the center of the
schmoo and set the memory drive currents accordingly.
I'm not going to try to draw a picture - but it really did look like
a (somewhat warped) schmoo. I never understood why the bumps for the feet
and head showed up, but they did.
Disclaimer: These opinions are my own and have |
nothing to do with the official policy or the | -bill
management of L.B.L, who probably couldn't | wlbrown@lbl.gov
care less about employees who play with trains. |