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!!!!!


Looking for additional LCD resources? Check out our LCD blog for the latest developments in LCD technology.

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