dil@lfcs.ed.ac.uk (David Laurenson) (11/17/89)
About a week ago I sent a message asking for help, namely... >I am trying to build a transputer link analyser that passively >monitors the communications link between two transputers, and produces >a high level (hopefully) form of debugging/performance monitoring. >I am currently trying to find a suitable differential driver/receiver >pair that I can use that will not introduce more than 3nS skew. I have received a number of replies, some of which were very helpful. I obviously did not make it clear what I was intending to do. I am going to use a C011 link adaptor to read in the link data, it is the electrical interface that I am worried about. I have had a number of suggestions about suitable chips:- Erik Johansson of Lawrence Livermore National Laboratory replies:- >Our links are buffered between boards using 74LS240s (or 74LS540s). >You could equally well use 74LS244s or 74LS541s. We use a 100 ohm >series resistor to provide impedance matching on the sending side, and >the signal is carried by a twisted pair wire with one side tied to >ground. On the receiving end, we use a 100k ohm pull-up resistor to >keep unconnected links idle (it is a pull-up because our logic is >inverted between boards). Although this scheme is not differential, >we have not had any problems with noise, and have driven the links at >both 10 and 20 MHz. David Boreham of inMoS replies:- >Try National Semiconductor parts DS8921A, DS8922A, DS8923A. >The best parts known are made by AT&T but are not generally >available. We have in-house link monitors and will be >bringing out a commrecial one in the next few months. And finally from Lyle Bingham of Computer Systems Architects, >You might investigate use of the National Semiconductor 26F31 and 26F32 >devices. AMD makes a workable set of differential buffers that we >have used for years. These are the 26LS31 and 26LS32. >If you can handle the speed, the optimum for skew is probably the >26C31/32 pair from National. Also of note is the National DS 8921 AN >differential driver/receiver pair. Thanks for all your help, and any further suggestions can be mailed to me at my address below. Dave. David I. Laurenson | Department of Computer Science | Edinburgh University King's Bldgs | JANET dil@uk.ac.ed.lfcs Mayfield Road, EDINBURGH U.K. |