I am trying to connect Unitronics Jazz2 PLC (JZ20-R16) and an Arduino Uno using 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). PLC is confogured to be Master, Arduiuno - 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 require DTR and DSR signals. As you can see from the schematic, the TTL-RS232 converter I've used can not provide such signals.
As You can see, CH3/4 (DTR/DTS) are required to be high in order for PLC to communicate over the modbus.But, as I've daid, the TTL-RS232 converter can not 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 +5V , no luck.