SPI Signal

Started by jasontje32 4 years ago4 replieslatest reply 4 years ago322 views
Hello Friends,

I am new to this Forum, so first  of all greetings to all !

I have an old Agilent system that has a detector and a DSP board. The signal is transmitted from the sensor to the board using a 40 pin flat-cable.

I have used a logic analyzer to determine if an SPI bus is being used to transmit the signals. I can see a number of clock signals (more then 10), However not a single MOSI / MISO Signal. I have also used an Oscilloscope on this. still no luck.

Is there someone who has experience with such systems. I would be happy to pay a small fee to someone who can guide this old retired hobbiest.

Best Wishes
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Reply by MarkSitkowskiOctober 13, 2020

You might try these guys:


(40 pins could be a 32 bit data bus with 5 address bits, plus R/W line, VCC and GND. If you can read the numbers on the IC's and any silk-screen text, it might help)

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Reply by stephanebOctober 13, 2020

@jbrower from Signalogic is a frequent contributor to this forum.  Maybe he'll have an idea...

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Reply by OZ1DUGOctober 13, 2020

It sounds like some kind of parrallel bus - A way forward is to find som datasheet on the DSP "processor". Can be that the "detector" is memory mapped into the DSP. 

Have you figured out the electrical levels (TTL, ECL, CMOS ...) and the electrical configuration (1, 2 or ? wires per signal/Bit). What are the signal direction on each wire ? (measure or track to a known IC pin).

Some Agilent (HP) system manuals and serviceinformation is free and can be found on internet. 

Apart form the "DSP" bord, this question is "off topic".

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Reply by KocsonyaOctober 13, 2020

Considering that SPI needs 4 signals plus ground, a 40-lane flat cable is not a very likely choice. Even if every second lane is GND, and a few used to deliver power, you still have a lot more than 4 signal lanes.

It can be a lot of things. IEEE-488 would come to mind as it was invented by HP, but even that uses only 24 wires.

You need to dig around the signals using the scope, but the simplest way would be to find a manual. Probably Google would be your friend in that regards.