RS485 --> RS485xRS232 Convertor --> GSM

M

Thread Starter

M. Bhamani

I have PLC programmed to send ASCII AT Command codes out through RS485 port.

When I connect PLC (two wire) ---> (two wire)RS485 to RS232 Convertor D9 Male ---> Male to Female adaptor ---> Cable D9F to RJ11 ---> GSM Modem (RJ11). It fails to initialise the modem. All my settings are correct 9600 8 N 1. I have following two questions:

1) On the RS485 to RS232 convertor I have dip switch that can set the Data Frame Length:

Start Bit + Data length + Parity + Stop Bit = 1 + 8 + 0 + 1 = 10 bit

which is also factory default setting. Is this setting correct for RS485 ASCII if my PLC has been set to 8 N 1?

2) I have a doubt on my cable between RS485 to RS232 Convertor [Cable D9F to RJ11].

a) Only 6 wires are connected on RJ11 side (7 & 8 are not comnnected). Is this ok?

b) Should there be a cross over between TX RX on either end i.e. Rx to Tx & Tx to Rx or should it be RX to RX & Tx to Tx? I have two such cables each having this type of wiring connections.Which one do I use?

Please advise.
 
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