Post by thread:I2C BUS MONITORING USING PICS

Hello All I have a query about an I2C Bus Monitoring PIC I am in need of some help, I am trying to get 2 PICs to communicate to each other using the I2C bus protocol. I have this partially completed and my results just outputted from PORTB (16C73A) to a 7 segment display. Now what I want to do is to connect a third PIC to non-intrusively monitor the data exchanged from the Master to the Slave. I have 2 ideas: 1. I could connect the third PIC to the Output PORTB which is connected to the 7seg display. Now the thing is I dont want the third PIC to send an ACK. to the other PICs (NON-INTRUSIVE). Been new to this I am not too sure if this can be achieved. 2.I could connect the third PIC to the output of the I2C bus from the Master to the slave, again I know that the slave will respond with ACK. but I, as I said before need the third PIC to be non-intrusive, just listen. If anyone has any ideas I would be really greatful, All the best Ken Finnegan (spam_OUTKenfinTakeThisOuTyahoo.com)

The short answer is, yes you can connect to an I2C bus using a PIC, and only monitor. I've done it, and it works. You can't use any canned I2C routines, or high level languages. Canned routines are intrusive, and High level languages are too slow. You hafta use assembly language, and straight line code, optimized to be as fast as possible. This is especially true if you are monitoring any HARDWARE I2C devices, not some slow-ass microcontroller. Hardware I2C is quite fast. Monitoring I2C is not too tough if you get the specifications figured out. Look for a start bit, and then look for the data you are monitoring in the results. {Original Message removed}