I picked up a K100D rather cheaply without pods. Looking at the service manual I discovered that each pod contained a custom hybrid circuit which was essentially a high-speed voltage comparator, and that the 5 connections back to the analuyser were ground, -5.2V, a differential ECL pair (signal input) and an analogue voltage from the analyser to set the threshold. A further connector on the back of the analyser provided +5V, -5.2CV and ground 'to power custom probes'. Well, 99% of my work is at TTL levels, and it didn't take too long to wire up some 10124 TTL to ECL level shifters to make a TTL-only pod. Not as nice as the real one with variable thresholds, but at least I could trace PERQ microocde, etc with it. -tony

Jochen Kunz wrote: I can't say I have done it, but an alternative to using (and finding) TTL->ECL chips would be to use standard voltage comparators. Devices such as the LM319 (dual high speed (80nS) comparator) could be set up with the comparators' ground at -5.2V and their supply at +5V (10.2V total supply for the comparators). One input to a comparator is a signal input, the other wired to a common voltage divider setting a switching threshold (hysteresis might be added with some more resistors, or use the threshold from the analyser). A resistor or two should should complete the interfacing between the comparator output and ECL input. This would have the added advantage of placing a far smaller load on the signal lines being tested. (A comparator input is a high impedance compared to the (rather large) load of a TTL input. (In the absence of ref data at hand I'm presuming TTL->ECL converter inputs are one TTL load.))

80ns is nowhere near fast enough!. That's about 12MHz, the analyser is a 100Msample/second unit... You want a comparator that switches in about 5ns... I did look into using analogue comparator chips, but at the time I did this (which must be 10 years ago) I couldn't find any that were (a) fast enough and (b) had enough input voltage range. I guess that's why the original Gould pods had custom hybrid circuits in them. Actually, the input to the analyser is a differential pair of ECL signals, but producing those is the easy part! They are... IIRC, I put some high-speed CMOS buffer chips between the circuit-under-test and the level shifters. Probably something like 74ACT245s with the control inputs tied appropriately -tony

On Sun, 21 Dec 2003, Brent Hilpert wrote: The AD8612 (dual comparator) would do - it has about a 4 ns propagation delay The AD8564 quad (a little slower at 7 ns) would reduce parts count. The MAX 9693 (dual 1.2 ns) with ECL outputs would avoid the TTL-ECL translator I've made input pods for my old HP 1650 (even made a little circuit card), But the 1650 input circuitry is in the main box, the input pods are just resistive dividers (like a bunch of passive scope probes all together) Peter Wallace

On Sun, 21 Dec 2003 11:10:00 -0500 Joe <rigdonj(a)cfl.rr.com> wrote: I have a LA5048 and it looks to be quite different from yours. I have no documentation for my machine. All I have is the pod pinout that a DLI employee mailed to me after I called the DLI tech-support. -- tsch??, Jochen Homepage: http://www.unixag-kl.fh-kl.de/~jkunz/

On Mon, 22 Dec 2003 21:20:14 -0500 Joe <rigdonj(a)cfl.rr.com> wrote: I don't have the address / phone number anymore. Note that the company "Dolch" is not related to the German "Dolch Logic Instruments", now knowen as "DLI". -- tsch??, Jochen Homepage: http://www.unixag-kl.fh-kl.de/~jkunz/