On Fri, Feb 3, 2017 at 8:55 AM, Adrian Graham <wit...@binarydinosaurs.co.uk> wrote:
> Ah yes, sorry, I'm aware of that. What I meant in this specific case is that > with 4 2764s right next to each other with a direct signal path between > adjacent address and data pins that has a resistance of 0.5 ohms pin to pin > surely I should be able to put a clip on each (for example) A4 address line > and see the same pulse at all four channels? Yes, subject to the following unlikely cases : 1) There is a standing wave developed between the pins. Technically that trace is a transmission line. I have never heard it happen between ICs next to each other at 8-bit micro speeds though. 2) There is a bad connection (IC socket?) on one of the pins 3) If you have a very fast logic analyser you might be able to see the propagation delay as the signal gets to each pin (remember a foot is about a nanosecond. So you are talking 10s of picoseconds delay). You will not see that with the sort of analyser you or I have :-) If you try your test with 4 of your logic analyser channels on the A4 pins of the EPROMs, I assume you get different traces for each channel -- that is what you are commenting on. What happens if you swap the logic analyser channels round? Incidentally, I'd better comment on the Logic Analysers I use. I use them a lot more than a 'scope, but that's because of what I generally need to do. 1) (Is is an LA?) The HP LogicDart. 3 Channels, 100MHz. No external clock facility. But it is pocket sized. HP called it the 'advanced logic proble' and that's really what it is. A better version of the blinking-light probe I used to use. Great for checking clocks, power supply voltages (it has a voltmeter function), serial data streams, etc. Normally the first instrument I grab for an unknown logic problem just to eliminate the 'sillies' 2) An old Gould-Biomation K100D. 16 channels 100MHz. with external clocking. I do have the 32 channel adapter for it which can only work with an external clock. This was my first LA and I still have a soft spot for it. 3) An HP1630. I forget which one, probably a 1630G. It does all I want. I was also AFAIK the last HP LA to have a proper component-level service manual. It's also a classic computer in its own right (6809 + 6829 MMU). Oddly the CRT is scanned vertically, I have no idea why. -tony
