GeoVision GV-R1352 Card Reader (13.56 MHz) - Manual (Page 82)

Appendix
What to do if RS-485 connection fails?
When a reader successfully connects to GV-AS Controller via RS-485, the Controller's Web
interface should show a green tick under Connection Status, and the reader's LED should
switch off from a continuous red.
If the reader's LED remains red and there is no successful connection status on the Web
interface, try adding a 180 Ohms terminal resistor on the RS-485 terminal block of the
reader to extend the range of data communication.
RS-485- _
+ Terminal Resistor
RS-485+