mc-Products => mc-Development Kit => Topic started by: rudydevolder on September 29, 2017, 02:05:52 am

Title: [SOLVED] I2C problem, only with Dev-board, when directly connected it works.
Post by: rudydevolder on September 29, 2017, 02:05:52 am
I have succesfully made a connection with a PSoc 4200 as a I2C slave with a McMod110 even at 400kHz ;D
But now I want to use the McDevelopment board it doesn't work any more.
I can see there are 2 LED's placed on that bus. So I presume the signal is BUFFERED and no pull-up resistors are used.
When I use my Digital scope to analyze what's on the I2C bus, I got a NACK. :(
But when I look on my analog scope I only see a noisy signals of around 0,5 Volts on SCL and around 200 milliVolts for SDA, clearly no pull-ups.
So I tried to add pull-up resistors, I tried everything 10k, 4k7, 2k2, 1k. I can see the signal improving by scope from 10k to 4k7, but at 1k I don't see much difference, the slope from the buffer is to slow I guess, even at 100kHz. I will try tommorow with lower frequencies because I think the buffer doesn't support high frequencies. Or is it safe to put lower value resistors?

[SOLVED] Read reply for this incredible story.

Title: Update: I2C problem SOLVED; UNBELIEVABLE
Post by: rudydevolder on October 03, 2017, 03:25:27 am
Everything seems to work.
The cause was just cables I crimped myself where 3 out of 3 badly connected on 1 side. I never had problems with my crimping tool, so I really trusted the cables. The fact that I had some signal although with lots of noise made me think it was only pull-ups missing. After studying the scheme and measuring the pins I found out the connection was direct, so it had to be the cable.
The only thing I can think about why I measured a signal is because high frequencies travel through air. I saw the pulses and the I2C Nack reply, therefore I was completely stunned to find out it was just the cable.
I had the cable crimped at a bad night being little sick. So there was to much of the insulator crimped and it didn't touched the wire.
Glad I finally found it. ;D ;D ;D
Lessons learned:
1. I will never trust my cables again and always test them first.
2. Signals travel through air, this can be very misleading. If I only had a good grounding connection I would see it immediately but none of 3 cables had really contact, so Murphy in his fullest glory.