Main Site Documentation

Wiring a parallel LCD using 74LS595N shifter


#1

Hi, I’ve been working on getting my parallel lcd to work with at little pins at possbile.

Other solutions on the web used the trick to use the shifter output to latch the E pin of the LCD, but the problem is that you have to enable the shifter twice. One to lower E, and one to raise E.

First I tried using separate pins for the shifters LATCH and the LCD E. After refactoring the driver it turned out to be doing exactly the same thing at the same time, so I just connected them together.

By slaving the LCD’s E pin to the LATCH pin of the 8 bit shifter, I save a roundtrip. The cool thing is that I still have 2 pins left on the shifter, and using only 3 OutputPorts.

(EDIT: Fixed some typo’s + explained its working perfectly)


#2

Would these help you:
http://www.tinyclr.com/downloads/Component/Broch_2x16LCD.pdf
http://www.tinyclr.com/downloads/Component/FEZ_Components_LCD2x16.cs


#3

Thanks for the attachments. I may have neglected to say I have it all working fine!

1 +5 PIN
1 GND PIN
D1 Data
D2 Clock
D3 Latch/E

I was just posting to tell about the Latch+E trick I used to save on digital pins.


#4

I use this method with the larger graphic LCD but it needs a delay buffer for faster latch speeds so I never thought to try it on a smaller character display. It’s good to know it works.


#5

Savitch… Slow down I haven’t got my PCB’s back for the second version yet…

Only joking!!! The second version was fast enough

Cheers Ian


#6

As a follow-up: The diagram above needs a patch.

I am using a 5v character LCD screen. When using external power instead of USB, I exceed the tolerances of the shift register. Therefore, all shift register connections need to be +3.3v instead of +5. Basically, only the backlight and the LCD logic should to be +5v.