slave writei2c
In this situations I use modbus (or mechanisams of modbus) or something similar (I do this on PLC's).
Master should put message:
ABCD
A - master address e.g. 01h
B - slave address e.g. 04h (third slave mcu)
C - command (give me temperature, or comething else, or put output pin 1 to "1" or ....), e.g. 01h give temp, 02h give time, 03h set output1 ....
D - checksum (there are many types of CS, so choose one...
Slave's should give answer:
ABCDE
A - slave address
B - master address (01h)
C - number of bytes which slave sending
D - data (C number of bytes data)
E - checksum
Regards,
Mr.Cube