Can anyone point out the differences between Standard RS232 and Modbus RS232?

 

RS232 is a hardware spec.

Modbus is a communications protocol.

--
Bob

 

Normally Modbus is on top of:
http://en.wikipedia.org/wiki/RS-485
That is you can connect several devices to the serial line. Where RS232 only allows to connect 2 devices with each other.

Modbus itself is a software protocol, that may use a serial line or TCP. It allows to address up to 254 slave devices.

If you use RS232 connections you can only connect 1 master to 1 slave.
With RS485 you can connect 1 master with up to 254 slave devices.

 

> If you use RS232 connections you can only connect 1 master to 1 slave.
> With RS485 you can connect 1 master with up to 254 slave devices.

Actually, I seem to recall there are several Modbus addresses that are reserved so you really cannot have 254 slave devices. I seem to recall there are 247 unreserved addresses, but I might be wrong about the actual number. If the number I recall is correct, the maximum number of slaves would be 246. But my rememberer might be wrong.