Scrambled characters and frozen display

mopedersen · Post by **mopedersen** » Wed Feb 15, 2006 6:57 am

Hi

Just bought a LK-204-25 serial display and I'm having some problems. Initially connected through RS-232 and got it working but all characters were scrambled - i.e. "A" always became "O", "C" became "N" not randomly but completely systematic. Tried all baud rates with same result, always the same mapping- Now, after some time the display has frozen at the startup screen, comes up but no response (tried cycling power a number of times)

Any suggestions ?

Post by **Aniso** » Wed Feb 15, 2006 9:12 am

For the time being, let us assume that this is a communication problem, but please check the power supply voltage with a multimeter and ensure that the power is stable at 5 volts +- 0.2V. If you are unsure of the power supply, you should look at it with a scope.

Start by getting the module unto a known state. You can manually override the baud rate by shorting the 2 center pins of the keypad connector (like with a shorting jumper) while the unit is unpowered and then applying power while the shorting jumper is still connnected. After power is applied, remove the shorting jumper.

The unit is now guaranteed to be listening at 19,200 baud. If you can talk to it at 19,200 baud, then you can issue a baud rate set command (see the manual). Once that is done, you should be able to cycle the power and still talk to the display. If any of this fails, please let me know.

mopedersen · Post by **mopedersen** » Wed Feb 15, 2006 9:29 am

Thanks for the reply. The supply is a floating lab. supply so the supply voltage is 5.00 V (checked with DVM). and the ground is connected to the RS232 ground wire. The jumpers are set for 19200 baud and I tried resetting it as you described. Unfortunately the result is the same, the startup screen is displayed and thats it, no connection to the module. (19200 baud, 8N1, no handshake) The weird part is also the letter scrambling when the communication was working, if noise was a problem I would have thought that the letters would be random but that was not the case.

Morten

Tom · Post by **Tom** » Wed Feb 15, 2006 10:09 am

Hi Morten,

Are you communicating at RS-232 voltage levels or TTL levels?

mopedersen · Post by **mopedersen** » Wed Feb 15, 2006 10:14 am

I am communicating with a COM port on a PC, i.e. at RS232 voltage levels

Tom · Post by **Tom** » Wed Feb 15, 2006 10:56 am

Have you tried another port to eliminate the factor that it is the problem with the port or device?

mopedersen · Post by **mopedersen** » Wed Feb 15, 2006 11:10 am

Yep, tried different ports (and different PC's)

Morten

Tom · Post by **Tom** » Wed Feb 15, 2006 1:13 pm

Can you measure the output of your com port and tell me if you are getting +-12V coming out, when you are sending some data?

Scrambled characters and frozen display

Scrambled characters and frozen display

Manual override