modbus RS485 RTS direction control



Is there a way to configure the modbus library to enable automatic control of RS485 transmit direction control when using the built in GX400 RS232 port to drive an RS232 to RS485 converter?

Many RS232 <-> RS485 converters require RTS (CTS OP on the GX) to be set when the host needs to transmit data - in hardware the RTS is connected to the RS485 driver direction pin

On a related note - is it possible to add additional USB TTYs by plugging devices into the GX400 USB port?

Thanks in advance




RS485 is being used as 4 wire(full duplex) or 2 wire(half duplex)?
In case of 2-wire RS485, Automatic direction control circuit enables driver when transmitting and disables receiver. Direction control can be automatic or controlled externally using handshake line (RTS). During marking or idle state, the RS485 driver is disabled and data lines are held by the 1k ohm pull up & pull down resistors.

I think there needs to be some kind of switch setting done in the hardware to enable automatic direction control.



The GX has a regular RS232 port. So if you enable hardware flow control, RTS pin should be acting as expected.

Regarding the USB, no alas, the GX does not support USB host mode for now, so it will not be able to use and external USB/Serial converter.