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I2C multimaster with devboard 82



I am trying to realize an I2C-bus-communication with
-PIC-Controller as a master
-EEPROM as a slave
-Devboard 82 as another master.

This means that two master are performing I/O-operations on the EEPROM via
I2C-bus. We are using the dedicated I2C-pins of the axis-board (PB0 and
PB1).

Now we saw on the oscilloscope that there are sometimes collisions, because
the axis-board does not recognize if the bus is already used by the PIC (the
PIC does recognize if the bus is used by the axis-board).
Furthermore the level of SCL never reaches LOW-level if the axis-board gives
HIGH-level (what it has to do in the idle-time), even if the PIC drives it
to LOW.
This lead us to the assumption that
1. there is no pull-up resistor used on the SCL-line on the axis-board
2. there is no busy-detection in the i2c-driver implemented.

My question is if there already exists a multimaster-i2c-driver or if we
have to modify the existing one ourself. And why is there no pullup-resistor
on the SCL-line? Well, it works in the single-master-mode, but it is not
usual.

Best regards
Martin