Clarification on RTS/CTS flow control (PH8) | Thales IoT Developer Community
May 14, 2014 - 4:05pm, 5083 views
Using the PH8 it seems that RTS/CTS flow control is not active by default, but practically mandatory. This is fine for us but the modem does not seem to be behaving according to my understanding of the V.24 standard.
If I power up the modem and hold the RTS line high (Request to Send inactive) no messages are sent by the modem, not even the ^SYSSTART power up message. I have to send RTS low in order to allow any messages to come from the modem.
As a result, it seems to me that the RTS is not actually equivalent to circuit 105 in the V.24 specification, as this circuit is intended to request the modem to wake up and prepare to receive data on TXD. Is it perhaps equivalent to circuit 133 (Ready For Receiving?)
Can anyone tell me what the recommended use of the RTS pin is when sending messages to the modem?
Looking forward to any suggestions, thanks!
May 15 2014 - 9:31pm
Hello,
you're probably using the module in power saving mode which is enabled by default. Change parameter value using AT^SCFG command to disabled. Please inform me if after changing operating mode the modem behaves according to your expectation.
Regards
Jedrzej
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May 16 2014 - 5:19pm
I am already turning off the power saving mode using the method that you have described, though I would prefer to have the power saving enabled for my application.
One of the first messages I send to the modem is AT\Q3 to ensure that RTS/CTS flow control is enabled (I know this is enabled by default on the PH8).
If I were to hold the RTS line low at all times, would that be a problem for when I am sending messages to the modem? I know that the CTS line must be active (0V) in order for the modem to receive the messages.
Can anyone recommend where I might find some timing diagrams showing the recommended signal states during transmit and receive?
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May 19 2014 - 3:21pm
Hello,
if your module is in power saving mode and it goes to sleep, this is indicated by CTS going up. There are two ways to wake the module up - sending new data (first byte missed) or set RTS on (toggle on->off->on if already on).
After the module wakes up CTS line goes down and you're ready to input commands. Now if you have hardware flow control enabled RTS line works like Ready To Receive circuit as you've already noticed - when CTS is active you're allowed to send the data and when RTS is active you signalize to the module that you're ready to accept new data. On the other hand when RTS is inactive all commands responses are buffered in the module to be sent to the terminal in the future. Holding RTS down when sending data is acceptable.
I hope I clarified this a little bit. You can find some more info regarding power saving and serial in HID document https://iot-developer.thalesgroup.com/documentation/ph8-technical-inform...
Regards
Jedrzej
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