Modem Auto Answer-Hanging for 1 min...

[Ioannis]

Trying to set up a modem, found that PIC 16F877 hangs for a minute or so when the program executes the Hserout ["ATS0=3",13,10] command. Monitoring the serial port I get:

ATS0=

and then the program freezes for a minute. After that, a string <00> follows!

ATX3
AT&K0
ATS0=<00>

Here is a snippet of the program:

hserout ["ATX3",13,10]
pause 500
hserout ["AT&K0",13,10] 'No Dial tone, no Flow Control
Pause 800
Hserout ["ATS0=3",13,10] 'Auto Answer in 3 rings
pause 500

If anyone has any idea what's going on here, please help!

Ioannis

P.S. I tried to send the commands as one like ATs=0x3&K0 and seems to work. I am just concerned about timing....

[Melanie]

Have you tried issuing a single command string?

hserout ["ATX3 AT&K0 ATS0=3",13,10]

Just wondering if you are trying to stuff the next command into the modem whilst it's still trying to acknowledge the first one you gave it. So increase the pause also.

[harrisondp]

Your PIC's input buffer may be overflowing, which may cause the pic to 'freeze'.

Add the following line if you don't already have one in your program:

DEFINE HSER_CLROERR 1

Harrison

[Ioannis]

Thanks for the replies.

Melanie:

Yes I tried to send the commands all together and it seems to work OK. But I do not know why, since there is no check from the program if the module has accepted the previous string...

I was thinking that the problem might be from the PIC itself side.

harrisonsp:
The command suggested is always included in my programs. Also the response from the module is set to be in numeric mode rather than in ASCII, so the flow is reduced to a zero for "OK".

Still mystery covers the case....

Ioannis

[Melanie]

No, I don't think it's the PIC. I would place money on it being the modem.

With a lot of modems with 'Hayes Style' command set, when you issue a command, the modem will reply (even if it's OK or just a plain CRLF).

It is possible that during this reply the PIC has issued the next command (intercommand Pause too short)... and in so doing the modem has lost part of the next command string receiving a corrupted sequence which in turn has caused it to timeout.

You could verify this by increasing the Pauses to something really long (eg PAUSE 5000 rather than 500) and see if it still hangs. If it doesn't, then that's the reason... your modem probably has poor firmware that can't simultaneously cope with a new command string whilst the reply to the previous one is still being processed.

Don't quote me, but I think there's a command to suppress these responses from the modem... you could always issue that first. That might also stop the problem.

[Ioannis]

Hmm, how much would you bed on it?? **smiles**!

The problem is still there. I just moved the sub's from top of program to the bottom of it and this part works OK now! Any explains? I usually put all sub's on top.

It is weird...

Ioannis

P.S. Of course half of the sub's do not work!!!