Hello Everyone,

I have a usb to serial converter (RS422) ,and would like to interface it with a sensor which communicates over RS485,it is possible to do it with my serial converter?If so please tell me the connections required and how do i give them for a full duplex mode?

The serial converter has an FT232 which is connected to a MAX488CSA.

PLease help.

 

What brand/model of converter? ask them?

 

converter was made by me ,basically it was for rs232 ,but we wanted RS422 communication cabability.I have never used RS422 before so i donot know how to connect it physically.

 

Edit:Attached schematic of the converter

 

If your device cannot tri-state (disable to hi-Z) the TX output, then you cannot use it for 485.

 

If your device cannot tri-state (disable to hi-Z) the TX output, then you cannot use it for 485.

I did not understand that.could you explain it more clearly with physical connections..(Where do RX+,RX-,TX+,TX- go...etc?)

 

RS-485 uses 2 wires to communicate bidirectionally.

You must be able to disable your transmitter to allow reception, your circuit cannot do that.

 

I see,thanks for clearing that for me
What do i need to modify to make it compatable with RS422?

Also if my slave is also a RS422 device how will the connections be set up?

 

You can add a MAX485 or equivalent IC (e.g. SN75176) to your existing design to provide RS-485 signalling.

If the USB-to-TTL converter supplies the RTS signal, you can use this to enable the RS-485 transmittter (and disable the receiver) via the /RE and DE control signals on the MAX485

Otherwise, you can use the first transition of TXD to trigger a monostable multivibrator in order to control the /RE and DE control signals on the MAX485. Set the pulse duration of the monostable to be just longer than the duration of one character. This may or may not cause a "turn around" interference depending on your situation.