LK204-25 communication problem

[stoledo]

I purchase a LK204-25 and I am having a problem comunicationg from my controller to the display and viserbersa.

I can use the PC to talked to the LK204-25 and I can get the keypad signals. I can get my control ( TERN i386 Drive)to talked to the PC and send data back and forth.
But when I hook the LK204-25 to my controller using the serial port at 19200, I can read the keyboard signals and able to send it back to be display, as long I don't hook the ground wire to the LK204-25.

To send data to the display I need to hook the ground wire. Then I can send data to the display but it displays garbage and ignores the commands such as clear the screen and others.

I try to use the TTL setup on the display and controller then I run into the same type of problem but a bit different. I can send data to the display, it executes the commands and displays correctrly but I can not read the keypad no matter what I do.

[Raquel]

Hello stoledo,

Thank you for your post.

Here are the connections I would expect for your controller and the module:

4pin Power / Data Connector in RS232:
1) +5V -- power +5V
2) LK204-25 Rx -- RS232 Transceiver Transmit out
3) LK204-25 Tx -- RS232 Transceiver Receive in
4) GND -- ground

4 pin Power / Data Connector in TTL:
1) +5V -- power +5V
2) LK204-25 Rx -- uC Transmit
3) LK204-25 Tx -- uC Receive
4) GND -- ground

It is important that there is common ground between the module and your uC. Make sure also that the settings on your uC are:
Baud = 19200
Parity = None
Stop Bit = 1
Data Bits = 8
Flow Control = None

Best Regards,

[stoledo]

Hello Racheal:

Thanks for responding.

I have check the connections for the TTL setup and serial and they work fine when talking to a PC. I do have the grounds tie together.
After I send the massage this morning I thoug of something could it be a ground problem.
I have done some checking by looking at the signals TX and RX with an scope and notice that when I do not have the grounds tie together the TX voltage level is about -7.5 vols and the Rx about +5.5 volts. Also notice that even hooking the ground from the scope makes the display start putting garbage on the screen.

I am starting to think there is a ground problem between the display and
my control. I run into this type of problem before and it turn out to be a ground loop. I am going to try to isolate the signals from each other.

Have anyone had a ground loop problem?

[Raquel]

Hello stoledo,

Ground loop problem is a tough one to deal with. Very unpredicatable at times. Unfortunately, I have not heared of someone here that has had the same troubles. Hopefully someone out there can shed some of their experiences and troubleshooting solutions.

You mentioned that you have encountered the same problem before, was it with the same uController?

Best Regards,