RS485-232 converter not working

[Rox]

rs485-232 converter circuit

I have made a circuit based on MAX3162 using Figure 9 of App Note 723 (Selecting and Using RS-232, RS-422, and RS-485 Serial Data Standards)
**broken link removed**

which is not working. I have shorted A-Y, and B-Z for 2-wire RS-485 connection. On the PC serial port connector I have shorted Data Carrier Detect, Data Terminal Ready and Data Set Read, and the pins used are Receive Data, Transmit Data and Request To Send.

The device with the RS-485 interface is the Iskra energy meter and I need to read the data on the PC serial port. The application used to view data is written in Java implementing IEC1107.

Please help to troubleshoot the circuit!

 

[cristianp]

rs485/232 converter + pin

What are the settings for your PC serial port? You should use hardware control with RTS and CTS connected together.

 

[Rox]

I am using COM2 on WinXP and using RTS as well. Do you mean to short RTS and CTS?

I am also using another PC in between for monitoring. The data is transmitted by the computer but nothing is received!

 

[IanP]

Start troubleshouting with simple things ..
Make sure that A is connected to A and B is connected to B and that they are not crossed over ..
Also, it is a good idea to add, in addition to the termination resistor, two bias resistors - one between A and Vcc and one between B and GND .. see picture below ..

Regards,
IanP

 

[artem]

Have a look to figure 8.
- Pins 17 18 are used for rs485 receiving, pin 12 is used to this receiver
- Pins 6 7 are used for rs485 output, and pin 22 is used to enable transmitter.

As you connected Z and Y to A and B - it means half duplex mode. Then you can see as pin 22 is always connected to Vcc means that transmitter is always enabled . You wont get any receive as transmitter will interfere with remote deivce's transceiver .

The rs485 transmitter has to be controlled fro your PC to select direction of the protocol converter. How ? Actually it is done using RTS line : assuming pin 19 is rs232 input driver , connect it to RTS line of the COM port and its output (pin 10) to pin 22 (transmitter enable pin). Of course, pin 22 has to be disconnected from Vcc first. Then choose transmit mode by setting RTS to 1 and receive by resetting it to zero.

Above assumed half duplex mode rs485 communication when only one device can transmit data in master slave style, where your pc is the master.