sms alarm

Dear all,

I'm using Schneider Modicon M241 and WAVECOM WMOD2(sms-module) to make a sms alarm. But now I am confused what communications protocol I should use, ASCII or Modbus. Someone told me I should use serial communication. Does this means I should use ASCII?

I have make a program like this, when I use HyperTerminal on PC, It can both receive and send message, but when connected to Wmod2, I can't get any response from Wmod2... I also don't know whether AT command has been sent to sms-module..

Is this problem occurred from no <CR> followed msg body? How to add <CR> after message? Then <Ctrl>+<Z> ??..

Can somebody give me some guide, Please!! Thanks a lot!!!

When we look at communication, RS232, RS422 is serial communication. The protocol is the information that is sent on the media. This would be similar to the paper as being the media, but the language written on it would be the protocol.
http://accautomation.ca/heres-a-quick-way-to-connect-rs232-equipment/
ASCII is just straight information being sent from the master to slave. (DTE - DCE)
http://www.asciitable.com/
Modbus is a specific protocol that uses a check sum calculation that gives an extra reassurance that information sent on the 1:N protocol is correct and no information is lost.
http://www.simplymodbus.ca/faq.htm

Since you are using Hyperterminal, separately connect it to the WAVECOM WMOD2(sms-module) to test the communication. If you are able to send / receive information then this is functioning correctly.

Next, connect Hyperterminal to the Modicon M241 serial port. If you are able to see the information on the screen that the PLC is sending then this is functioning correctly.

The final step is to then connect the PLC port to the WAVECOM WMOD2 and test your program.

Hope this helps you out.
Regards,

Dear Garry,

Thanks you first.

I have already used the program I posted to test it step 1 and 2 you mentioned. but the final step can't work. Could you help me analyze what problem is?

Kind regards,
Ryan

Hi Ryan,
What happens when you connect the PLC and WMOD2 together?
On the PLC side are you receiving any information from the WDOD2 after you send information out?

Hi Garry

There is no information from WMOD2 after I send AT. I also tried to add <CR> after AT, there still no information from Wmod2.

Ryan

There should be some indication lights on the PLC. Do you see this turning on when sending the data? or receiving the data?

Are there indication lights on the WMOD2 that shows when information is being received or sending?

You should try exactly what you did with Hyperterminal. If you typed AT and then CR then in the PLC you should send the equivalent ASCII code for 'AT' and the CR.
When the PLC was connected to the Hyperterminal and you sent information from the PLC. Did the screen show the AT characters and then the cursor was underneath the AT characters or was it beside? This will indicate if a carriage return was issued or not.

I do try exactly what I did on HyperTerminal to test wmod2. But nothing happen, light on M241 and Wmod2 also don't turn on.

When the PLC was connected to the Hyperterminal and you sent information from the PLC. And the cursor was beside the AT characters.

Hi Ryan,
Did the lights turn on/off when you tested each of the units with Hyperterminal?

Since each of the units connect individually to Hyperterminal, we know that the communication baud, parity, stop, data bits are correct on each end. The cable connecting the PLC to the WMOD2 is still not proven. Do you have the pinout of the cable being used, and the pinout of the serial port and WMOD2 port?

When you connected the Hyperterminal to the WMOD2 did you have to send the AT and then hit the carriage return to get the OK to be displayed back to you?
If so then add the ASCII character 13 decimal (0D Hex) to the string that is being sent out from the PLC.

Regards,