Question

Using RUT955 RS232 port in 'modem' mode outbound connections work fine, but the legacy devices I would like to support do not recognise the 'RING' string from an incoming connection, instead they use the analog modem 'auto-answer' function (controlled by 'ATS0' command) to accept incoming calls. It's not practicable to reprogram these old units to change their behaviour. Is there any simple way to add auto-answer functionality ( in effect, issuing the 'ATA' command to itself when it issues the 'RING' string) without building special non-standard firmware for it ?

Answer 1

Hello,

We are looking at this case and will inform you when have any information.

Comments

Hi Tomas,

Thanks for that. I have made some progress on this myself. I uploaded the source code last weekend and after some searching found the relevant file ( modem_core.c, I think - I'm not at the right machine to check exactly) which suggested that the modem function probably supported more AT commands than the very limited subset that are documented.  I experimented and found that putting the auto-answer enable command  'ATS0=1' into the router modem configuration as initialisation string had the desired effect and seems to have resolved the immediate problem.

One thing to beware of is that making any change to the router RS232 settings through the web GUI appears to cancel the effect of the initialisation string; a router reboot is then needed to restore the previous auto-answer state. I'd presume this would apply to any other 'ATS' setting too.

It would be very useful if the scope and limitations of the 'modem' functions support for AT commands could be more fully documented. Glancing at the code it looked as though several other commands might also be supported, but I don't have enough knowledge of the overall firmware architecture to decide if that could be relied on without a lot of empirical testing.

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Hi Tomas,

I spoke a little too soon, it seems. Although the 'ATS0=1' command as initialisation string works after a forced reboot from the WebGUI 'System' menu, the effect seems to be lost after a power-down cycle. The string is still there in the RS232 setup page but the port issues repeated 'RING' strings and no longer auto-answers.

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Hi,

To avoid resetting ATS0, instead of using "Initiation string" in RS232 parameters and entering command there, go to System -> User Scripts and before "exit 0" enter "gsmctl -A ATS0=1". This will ensure that after each restart or power cycle router modem will be configured to auto answer a call.

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Hi Tomas,

Thank you, that looks to have fixed the auto-answer problem.