Hi: I have a Digi One IAP that I am trying to use to link up a ModBus PLC (Rs232, RTU mode) with a scale which is ASCII, RS232. I cannot communicate with port 1 in RS232 mode, and I have noticed that the voltage on pin 2 is -7V. This is not normal for an RS232… (pin 3 is also at -7V). Do I have a hardware problem or am I missing something in the configuration? I know I am not communicating because the stat page on the device is all zeros. THANKS!
Port 1 Pin 2 (screw terminal) is DTR, so -7v is just fine for RS-232 which wants +12 to +3 or -12 to -3 vdc … but -7v indicates that the DTR is low/off.
Port 1 Pin 3 (screw terminal) is TxD.
I think you may be reading the label incorrectly - pin #2 on the DB9 (port 2) is not connected to pin #2 on the screw terminals (port 1). The layout is different.
I think the rather unusual layout of the screw terminals is due to some legacy product that existed before the DOIAP existed as a product.