I am trying to connect a Unitronics Jazz2 PLC (JZ20-R16) and an Arduino Uno using the Modbus protocol, over RS232 interface.
I've got all the required connectors for both Arduino (TTL-RS232 MAX3232 converter as the one below) and Unitronics (JZ20-PRG with JZ10-22-CS10 RS232 connector).
The PLC is configured to be master, the Arduino is slave. Configuration is 8N1. Both units operate very well while connected to ModbusSimulators (from modbustools.com).
I connect these devices to the PC using a RS232-USB converter. The problem is that the PLC requires DTR and DSR signals. As you can see from the schematic, the TTL-RS232 converter I've used can't provide such signals.
Here's the screenshot of succesfull data stransfer between the PLC and a PC simulator:
As you can see, CH3/4 (DTR/DTS) are required to be high in order for the PLC to communicate over Modbus. But, as I've said, the TTL-RS232 converter can't give high DTR/DTS signals. Any idea if there is a chance to tweak this? I've tried to hook DTR/DTS pins of the PLC to +5 V, but no luck.