2-wire RS485

Question

We can't send data to a port configured as 2-wire RS485 on the port sever TS16 MEI from the field device. We can send data from the Linux application to the field device via the port server. But when the device sends the response back, it never gets to the port server (0 bytes shown on the port server web page). When a commercial kit (USB-COMM485-PLUS) is used to test, it can receive data from the field device. We already set the TXCONTROL to AUTO as per the documentation. It doesn't seem to help. Any pointer would be really appreciated.

Answer 1

This sounds like a possible cabling issue. Recommend confirming the cabling is proper from page 33 of the following cable guide:

http://ftp1.digi.com/support/cabling/90000253_E.pdf

Knowledge base article link:

http://smax.digi.com/kbase/kbaseedit.aspx?kbid=3489

Answer 2

Thanks for getting back. We were using the wiring table shown on that exact page.
TxD(A)/RxD(A) Transmitted/Received Data (A) 4
TxD(/RxD( Transmitted/Received Data ( 5
GND Ground 6

Since TX & RX share the same pair, the fact that we got the TX part work correctly indicates the wiring is fine. We still have no idea why RX does not work.

Answer 3

I am having a similar issue. if the cable used is longer than ~20 m the communication doesn't work but the communication seems to work fine with a short cable. when replacing the portserver with an interface, wether usb-rs485 or ethernet-rs485, the communication works very fine. is this a limitation in the portserver or am i doing something wrong.

Answer 4

may be it is wrong or not working. try out again.

Answer 5

there is some issue in cables thats why it works not properly.