Character LCDs - Info. and Links
I've had a few emails from people having problems whilst building my keyboard viewer, or using my LCD driver code for their own projects. This page is to help anybody in a similar situation.
The main problem tends to be that the display contrast is not set correctly,
or that they have used an extended temperature range display without realising
that it needs a negative contrast voltage.
Another problem is that emulators and character LCDs don't seem to like each other - try a windowed device and it may work.
Character LCD tester - This code simply checks an LCD and wiring is working correctly, and indicates on an LED what faults were found. Tests any character LCD display based on the HD44780 or compatible controller.
Compatibles believed to be, but not tested:-
- Samsung KS0066
- Sanyo LC7985 NA
- Epson SED1278
- UMC UM3881B
- OKI MSM6222
- Toshiba T7934-0000 (has extra characters in CG ROM )
- NewJapanRadio NJU64xx (various)
Indications repeated every 4 seconds :-
- constantly on or off - PIC not running, or not programmed correctly, or
LED not wired up correctly
- 1 x 1/2 sec flash - all GOOD - LCD working correctly.
(if display not readable, alter contrast)
- 2 x 1/2 sec flashes - Pins shorted / wired wrong.
(After setting the signals to the LCD, they read
back differently)
- 3 x 1/2 sec flashes - LCD busy too long or no display attached.
(After waiting long enough for an LCD instruction
to have finished, the busy flag still reads as busy)
- 4 x 1/2 sec flashes - address readback incorrect - check data wiring.
(After setting LCD to auto increment character
address, read back character address is different
to that expected)
When correctly connected, and contrast set correctly, part of the character
set will be displayed on the LCD.
Links to Useful Web Pages
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Steve Lawther
Last Updated by Steve Lawther on Tuesday, 4 August, 1998 at 10:35 PM.