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red X key causing reset or reboot of CFA635


New member

I'm using the CFA635 with serial interface. I'm using the red X key (on release) to allow the user to toggle back and forth between two 4x20 pages of information. All works well with one exception:

Frequently, when I press and release the red X key, the CFA635 reboots. There doesn't seem to be any specific parttern. Whether I hold the key down a long time (several seconds) or a short time (a second or less), the reboot seems to occur at random.

The problem seems to have something to do with GPIO/ATX functions. Maybe there is a configuration problem. I've reviewed commands 28 and 34 closely, but I don't understand how to cofigure the keypad to prevent the problem from occurring (if these functions are relevant to my problem).

Any suggestions would be greatly appreciated!!!!!


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CF Tech

Well, it certainly should not do that.

Please note that after changing commands 28 (28 (0x1C): Set ATX Power Switch Functionality) and 34 (34 (0x22): Set or Set and Configure GPIO Pin), you must use command 4 (4 (0x04): Store Current State As Boot State) to save the setting if you want the new setting to become the default.

Can you answer some background questions?

Is this in a PC?

What software is talking to it?

Can you duplicate the problem if the only software you are using is 635_WinTest?

It could be that there is some mechanical fault on the module. Perhaps pressing the key breaks some other circuit somewhere.


New member
answers to questions

Thanks for the comments & questions.

I'm driving the LCD/keypad using a microcontroller (Atmel AT89C51ED2) interfaced via an off-chip UART and TTL-to-RS232 converter. As I think I said previously, all messages to the LCD and keypad operations work well--except for the glitch with the red X key.

I'm driving the LCD/keypad using C functions that I've written myself.

I don't think there are mechanical/electrical faults. I have the LCD/keypad installed in two different instruments, and both experience the same glitch. So, I suspect a software problem.

Although I metioned commands 28 and 34 in my original post, I have not output either of these commands to the CFA635. I don't understand enough about them to know what to output.

I haven't tried using WinTest to reproduce the problem at this time.

Thanks again for your input.



New member
red X key causing reboot --problem resolved


Embarassingly, I have finally found that the problem was not with the CFA635 but with my software. When I pressed the red X key, I caused additional code to be executed so that my software cycle exceeded the watchdog timeout for my microcontroller. This caused the microcontroller to reset. When I added a couple of restart_watchdog() statements at strategic places in my code, the problem was resolved.

USB LCD Displays - Graphic and Character LCDs with a Keypad