Basic Interfacing of HD44780 based LCD with PIC16F84

Basic Interfacing of HD44780 based LCD with PICs.

After spending 2 days familiarizing myself with PICMicros by making LED circuits blink, I decide that it was time I take a step further in PIC Projects. What better choice there can be other than interfacing a PICMicro to an Liquid Crystal Display (LCD) unit. :)

I bought my LCD from Electronic Inventory Online (EIO) store, which website is located at www.eio.com. They sell quite a variety of LCD for an affordable price too. I bought myself 3 units of Seiko L1642B1L. They are the older variant of the newer 1682 16x2 LCD units. The only drawback about this LCD is that this LCD unit seems to have low level of contrast. Even at maximum contrast, you can barely see the text on the LCD screen. To correct for this problem, I used the LCD's backlit to get a better view of the text on the LCD.

The datasheet for all Seiko Instruments LCD can be found here, at Seiko Instrument's website.

Presented here are the source code and the schematics for this project. The code is written according to the instructions shown in the datasheet. The source code is quite clearly documented and remarked so there isn't really a need to explain about its operation over here. Also included are some pictures I took on the circuit.

Source code : seikolcd.asm

Although this code works, there is alot of room for improvement since this was like the.... 6th programme I wrote in PICMicro assembler :D. For instance, we can reduce on the delay time routines. I put larger number of loops to make certain that the each instructions written to the LCD has sufficient time to be completed before executing the next instruction.

Then, I decided to write a more optimized code than the above by reducing the size and the execution time of the programme by using shorter delay time. This way the the instructions executed faster and at the same time, has sufficient delay to complete its execution. Presented below are the new schematics and source code. This code is written for PIC16F873A instead of PIC16F84. Just change the connections from PORTB to PORTC for the LCD datalines DB0 to DB7 and the RS, R/W and E lines from PORTA to PORTB. It can be used for any other 28 or 40 pins PICMicro such as the PIC16F873, 876, 876A, 877, 877A and etc. by changing the **include 'p16f84.inc' to p16f873a.inc and the connections pinout.

Presented below are the source code and the schematics for the PIC16F873A interfacing.

These simple programmes can be used as a display test of the LCD before actually starting on a project that requires the use of the LCD. This way you can be certain that the LCD actually works before implementation. I will improve on these source codes and implement them in future PICMicro Pet Projects. :)

Source code : seikolcd873a.asm

A more optimized and faster code ==> seikolcd873_2.asm

For the seikolcd873_2.asm code, the pinout is slightly different. The data pins (DB0-DB7) now goes to PORTB of the LCD while RS, R/W and E pins now goes to Pin RC0, RC1, and RC2 respectively. I also included a picture of the circuit built using the above code below.

I also wrote a C version of the code. It is compiled using HiTech C Compiler. This interfacing method utilizes the 4 bit mode of the LCD and a PIC16F877A as a CPU. Therefore, the schematics may have to be modified according to the instructions on the source code files. The source code files zipped below.

Source code : asd.zip

This is coded in HiTEch C.

Last Updated : 22th July 2005, 4.00am Eastern Time.

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