| Electronics > Repair |
| Fluke PM6666 counter freezing after 3 seconds from turning on. |
| << < (23/27) > >> |
| khs:
Now I've learned a device can stop I²C communication by holding SCK low. So here my suggestion: What happens when we insert a SCL buffer between the SCL output of the microprocessor and the GPIB controller , so the I²C bus cannot stopped by the GPIB device holding SCL low? Not to destroy the SCL input/output of the GPIB device I would insert about 100 Ohm between the output of the buffer and the SCL input/output of the GPIB device. |
| thinkfat:
--- Quote from: khs on October 15, 2020, 11:00:04 am ---Now I've learned a device can stop I²C communication by holding SCK low. So here my suggestion: What happens when we insert a SCL buffer between the SCL output of the microprocessor and the GPIB controller , so the I²C bus cannot stopped by the GPIB device holding SCL low? Not to destroy the SCL input/output of the GPIB device I would insert about 100 Ohm between the output of the buffer and the SCL input/output of the GPIB device. --- End quote --- Violation of the I2C bus protocol. A slave must be able to stall the master when it needs more time for processing the access. This is called "clock stretching". If the GPIB card stops the counter from working I'd just remove it. It doesn't work anyway so it doesn't make any sense to have it. |
| 0xdeadbeef:
Dunno when/if I'll find the time but I'll consider it. Is this Pin19 of the IC marked L5899MC? |
| pizzigri:
Well it's pin 19 of the custom ASIC labeled 0Q0501P, but yes, it's the same chip. It's interesting to note markings, this IC was built in week 34 of 1997 in Nijmegen Holland, then sent to Taiwan for assembly and again tested in Holland. |
| pizzigri:
--- Quote from: thinkfat on October 15, 2020, 11:25:17 am --- Violation of the I2C bus protocol. A slave must be able to stall the master when it needs more time for processing the access. This is called "clock stretching". If the GPIB card stops the counter from working I'd just remove it. It doesn't work anyway so it doesn't make any sense to have it. --- End quote --- Thinkfat, therefore I think that this will place a nice nail in the coffin. I am wasting too much of the precious time of all EEVB members, and I am extremely grateful for all your help, at this point I will just remove the GPIB card for good and close the meter. Maybe I'll use the option connector on the M/B as convenient way to power a OCXO inside the unit, simply routing the output externally using a 4cm BNC patch cable, the meter will see it as a External ref, and that's it. But it has been a great ride, and I have learned a lot! Just for info, I will remove the CPU once I get back home and see what the clock looks like without it... All my best, Franco |
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