Alarming problem

[Early1]

Two years ago I built an alarm unit using the flash lab system with a 18F452 running at 20Mhz. It has been in the field on different construction sites since then and has worked flawlesly.

I have built a second one using the flash lab again but with a 18F452 running at 40Mhz. The only other change is the LCD was a 2x16 and now is a 4x40 serial LCD. The keypad the LCD the menue sytem all work as expected but I can not get the GSM modem to send the text messages, which makes the alarm useless.

Surely it can not be the change in chip speed that is causing the problem?

I have tried serin2 serout2, hserin hserout, I have put delays in the instructions and pauses in the program. I have checked and changed about every AT command on the modem and nothing changes.

I have used the LCD to debug the program and the PIC does not seem to be getting any replies from the modem, except the first one. I send AT to the modem the modem replies with OK and the program continues to the next instruction which also requires a reply from the modem and it just stops there.

I have connected to the flash lab with hyperterminal and when I type in the expected replies the program runs and when I use hyperterminal connected to the modem it works as expected. They just will not talk to each other.

???????

Steve

[paul borgmeier]

Oops - After rereading your post, I have no idea - my apologies for the false hope

Paul Borgmeier
Salt Lake City, Utah
USA

[Jerson]

But, recently, I had a similar problem with the baud rate on a different chip. I had the prototype working consistently and everytime on every board I built. But, all the other chips I managed to program did not work. I thought I had bad chips and tried to reconfigure and play with the settings. Everytime the result was just the same. The very first chip(proto) worked well irrespective of the code changes, the others wouldn't. Finally, I narrowed it down to the baud rate. The divider count was off by 1 count. Since you said that you changed the clock to 40MHz, perhaps you could check on the baud rate settings. Perhaps the 40MHz is off???

Jerson

[Acetronics2]

Hi, Steve

few weeks ago,I read on this forum the PLL clock of the PICs was not working so well ... and was very sensitive to power variations.

...

Alain

[Bruce]

Does the new one work if you switch from 40MHz to 20MHz?

[Early1]

Thanks Guys

I have come to the conclusion that faster is not necessarily better. I have read and re-read the 18F452 data sheet and my impression is that at 40Mhz I should be using a higher baud rate but years of using GSM modems at 9600 has taught me that this is a safe reliable connection speed.

Bruce I have ordered a 20Mhz Flash Lab and in due course all will be revealed.

Cheers