Wiring LCD Parallel in-bit mode

kenwtn

··· Always double checking myself and apologize to all those of you that get stuck reading my dumb questions. OK from the schematic I have PINS 4,5,6, and 7 provide the 4-bits of data. Then the other 4-bits on the LCD are connected straight to ground. Can someone tell me if that is correct? I saw one schematic that did not connect those 4-bits pinouts to anything that would be easier but does not make much sense to me. As you can tell I am far from a electronic wiz.

kenwtn

I should clarify the PINS 4,5,6 and 7 I refer to are coming from the basic stamp and connect to the pinouts 11,12,13 and 14 of the LCD.

bobledoux

For a Hitachi HD44780 controlled LCD in 4-bit data mode, LCD data pins for data bits 0, 1, 2, 3 are grounded. These correspond to LCD pins 7, 8, 9, 10. You can also ground the read/write pin 5 unless you need to use the LCD for data storage. Some LCD's work well when the contrast, pin 3, is grounded.

This leaves you with just 6 pins required for control, the 4 data pins, the enable pin and the register select pin. Don't forget ground and Vdd.

kenwtn

That is very helpful. I got one addtiional question. The LCD I have is 16 pins with backlight option and I did not find on the schematic how to connect those. Any ideas?

Chris Savage

If the LCD is LED backlit then one of those pins will be ground (Cathode Terminal) and the other will be V+ (Anode).· You will need the datasheet for that display to determine the backlight forward voltage and current to pick the correct resistor to run it from the supply voltage.· I have seen these values vary from 2 ohms to 100 ohms depending on the display.· Then again your display could just as easily have a CCFL or EL backlight, in which case you would need an inverter.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Chris Savage
Parallax Tech Support
csavage@parallax.com