drjohnsmith
Well-known member
I'm fishing here ....
Have a few teensys here, running,
using them to interface to I2C chips / things.
So I know about capacitance, rise / fall times, signal integrity, I2C speed,
But have a problem,
I increase the cable capacitance, and the I2C fails.
But when I look with nice fast scope,
I can see that the teensy is receiving what is still within in the old philips I2C rise / fall spec,
The I2C is failing when I hit around 200 ns rise time due to the pull ups.
I've looked at the timings of the pulses, and all looks well within the I2C spec,
I'm using t3_i2c for the wire library , but seem to have similar results with the standard wire library.
I've got some way to go on this ,
yes look at pull ups, check for glitches on the data / clock lines, may be I2C re generator,
but the signal just does not look half a sick as I2C I have seen working,
was wondering,
how I2C compliment is the I2C library ?
As I said, it works fine over short cables,
but was wondering about things like I2C glitch filters, does the cpu have them and are they turned on by default ?
does the teensey cope with the slow edge, wonder if the teensy is multiple triggering by the slow edge,
Don't know, and a long way to go , but as I know nought about the teensy code I thought I'd give a quick ask in case some one goes ah yes..
Thanks
Have a few teensys here, running,
using them to interface to I2C chips / things.
So I know about capacitance, rise / fall times, signal integrity, I2C speed,
But have a problem,
I increase the cable capacitance, and the I2C fails.
But when I look with nice fast scope,
I can see that the teensy is receiving what is still within in the old philips I2C rise / fall spec,
The I2C is failing when I hit around 200 ns rise time due to the pull ups.
I've looked at the timings of the pulses, and all looks well within the I2C spec,
I'm using t3_i2c for the wire library , but seem to have similar results with the standard wire library.
I've got some way to go on this ,
yes look at pull ups, check for glitches on the data / clock lines, may be I2C re generator,
but the signal just does not look half a sick as I2C I have seen working,
was wondering,
how I2C compliment is the I2C library ?
As I said, it works fine over short cables,
but was wondering about things like I2C glitch filters, does the cpu have them and are they turned on by default ?
does the teensey cope with the slow edge, wonder if the teensy is multiple triggering by the slow edge,
Don't know, and a long way to go , but as I know nought about the teensy code I thought I'd give a quick ask in case some one goes ah yes..
Thanks