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LCD driver and 20x4 LCD


I’ve been playing with a lontech LCD driver: RS-232(2004) Driver
And I’ve attached it to a Hitachi 20x4 LCD: HD44780U (LCD-II) (Dot Matrix Liquid Crystal Display Controller/Driver)

Once again I’m a little confused as as to why I can’t get it this serial device working.
I decided to connect it to the USB->UART (RS232MAX) cable instead of my domino, so I don’t burn out my last two remaining serial ports. ::slight_smile: These cables are cheaper than my Domino.

The Driver feature says: Communicate over RS232 interface
It has a MAX232 chip on it, see attached image.

LCD driver datasheet

On page 6 of the datasheet it also says:

[quote]RS-232 Communications
The RS-232 connector on the PC cable is wired so that a standard “straight through” 9 pin D-sub cable
may be used to connect the module to a standard serial port such as COM ports on PCs. Note that this device
complies with the EIA232 standard in that it uses signal levels from ± 12V to ± 12V and can be converted to
TTL levels as well. The LCDRS2 is set at 9600 bps default speed. Other settings are:
8 bits, no parity, 1 stop bit.
DB9 Connection
A standard DB-9F is provided for RS-232 communications. Power may also be supplied via this connector
if desired.


I have attached the description from page 6.

I’ve set the connect speed to 9600bps, as I’ve learnt this from previous mistakes.

So I guess my questions are:
Is the output from the LCD driver RS232 or UART (TTL level)?
Have I stuffed the USB->UART cable?
How do I get it working with the USB-> UART cable.


I’ve also attached photos of the connections.

  • USB->UART (Out -White) : LCD Driver in (J3 pin 4)
  • USB->UART (GND -Black) : Domino GND
  • LCD Driver 5V (J3 pin 1) : Domino 5V
  • LCD Driver GND (J3 Pin 2) : Domino GND

Let me know if you need more info.


After a chat with hobeau It looks like if I connect to the J3 pin MCU-RXD it should accept TTL level signals. I give an update on how this goes soon.


Ok, that failed. The Back light comes on randomly, that’s about it.


I tried using the USB->RS232 cable (reluctantly) and still no luck.

The back display turns on and off depending on what message I send, but that’s it…


I think I found the issue, I think I should be using J1 instead of J5. I’ll post back soon on how I go.
That’s the problem when you look at pictures instead of what is written. The Driver datasheet pictures are not helpful at all. And the fact I didn’t find a datasheet for the LCD until now.




I think if you want to use TTL you want pins 5 and 6 on the header… 3/4 are rs232.