Hi Jacqmaster,

It sounds like somehow the EEPROM in your display module has been corrupt. By default, the keys should be transmitting those that are depicted in the tables on page 40 of the manual .

By using Assign Keypad Code command (254 / 213) you should be able to assign any values that you ...

If you have a steady hand you can also move the zero ohm resistors on the back of the module from rs232 to ttl.

Finally, I added one MAX202 circuit and it works greats. But I got another while connecting to a 4x4 keypad. When I short R1-C1, the LCD will display 246, R1-C2 =>61.
How can get read ...

Ray wrote:I suspect the Arduino is operating on TTL levels

Thus, I just need to add MAX232 driver between Arduino and LK204 to converting the voltage level, am I right?

THanks,

I just bought the LK204-25 and its default setting is RS232 mode.
I connected the LK204-Rx pin to Arduino Mega Tx1 (Serial1) and get 5V power from Arduino as well.
When power up the module, I can see the default startup screen.
But when I run the below tiny program, the result totally awkward ...