I am in the process of developing a prototype that connects 4 Arduino boards to an HMI using MODBUS.
In the past I have built several small systems using Arduino and MODBUSslave library. There is a great tutorial I found by krak, but this is limited to only connecting a single HMI to a single Arduino.
- Board: Arduino UNO
- HMI: EA9-T6CL-R running C-more
- Converter: TTL to RS232 Converter
- COM Cable: DB9 to DB15 Cable
I imagine that I can connect many more Arduino boards to the same HMI as long as they have unique device IDs. Hopefully, with some help I can get this to work. Before starting I was wondering if I could parallel all the TX/RX lines together into a TTL to RS232 (max232) converter. Then this converter has a cable that plugs into the HMI. Is this possible or do I need some termination resistors?
Also, is hardware flow control necessary? I have CTS/RTS pins closed and not currently being used. I am worried that these devices will not be able to talk simultaneously. In this case I would consider using RS485.
For what it's worth I am running at a low speed (9600 baud and 30 kb/s).
Any help is appreciated. Thanks!