I am using a Digi IAP connected to two Allen-Bradley PLCs. After power failure, my Digi One IAP sometimes comes up in single serial port mode instead of two, even with the Pass-Through switch set to ON. I have had to disconnect the serial cables and power on two get the IAP to recognize two serial ports.
Are these by any chance PLC5? Rack KE/KF cards with DF1 ports? Does the DOIAP seem to get warm to the touch?
Without going into too much details, the SIBEX interface chip used in the Digi One IAP has proven not very happy with voltages higher than 12vdc (RS-232 is supposed to operate up to +/-15vdc I think). This chip is being designed OUT of the product, but that takes time as it’s a very unique dual 232/485 chip. One usually assumes a commercially produced & marketed RS-232 chip actually supports RS-232-like signals.
I have dealt with 2 other customers with the PLC5 addon DF1 cards who had to not use the DOIAP because they would heat up and fail, so I assume these PLC5 cards run a solid 12+ volts to gain extra distance.
These are a PLC5 and a PLC2 right? It would be useful to see the Txd voltage of the PLC2 compared to its SGnd (which ever PLC is on 2nd port) when no cable is connected. This should be the highest voltage it creates as it will have no load to draw it down.