In the previous part, we saw how to instruction set works and how the different pins fit together to make the GLCD work. In this part, we’ll pick a particular microcontroller and try to work out how to configure the pins.
The JHD12864E works in a parallel mode. By parallel, I mean that the data is passed in one shot which is by the data pins D0-D7 on the display. There are other GLCDs which pass data in serial i.e. one instruction at a time. In this case, we don’t need so many pins but there will be other considerations that we will need to … uh … consider.
Now that you’ve got the GLCD up and running and probably tried a few things, you’d like to put a picture of your cat on the display and see if he/she can recognise it right? It’s okay, you can admit it, I’m not judging.
This can be broken down into 2 steps:
1. Convert an existing image into a 1-bit black or white bitmap (BMP) image
2. Convert the bitmap from the previous step into an array for use with your microcontroller
Step 1 – Convert an existing image into a 1-bit black or white bitmap (BMP) image
This part explains how to pass instructions/commands to the GLCD. On a high level, these are the steps:
- Select the GLCD half-section
- Put the Enable Pin LOW
- Put RS, RW and Data pins HIGH or LOW based on your command
- Put the Enable Pin HIGH
- Wait 2 milliseconds
- Put the Enable Pin LOW
- Wait 2 milliseconds
- GLCD responds
And you’re done! Easy-peasy!
Well, not quite. Let’s look into each of these steps in a little more detail. Here’s an image from the last part for quick reference:
The GLCD has a 128×64 resolution. This equals about 8192 individual pixels that you can control as you wish. But how is this done? Let’s see how we reach a particular pixel on the screen.
The LCD screen is actually divided into 2 halves with one KS0108 IC for each half. Each KS0108 IC has the ability to control 64×64 pixels, so both of them side-by-side should be able to give you the complete resolution of 128×64. So, by choosing which one of the two ICs, you can narrow your pixel down to one of the two halves.
Next, each half containing 64×64 pixels has an addressing scheme using the Y address and X address as follows. Lets start with the columns. Each half has 64 columns numbered from 0 to 63. Straightforward enough, not too much to get confused about, each column is addressed using the Y address which ranges from 0 to 63. Continue reading
The GLCD (Graphics LCD) display that I’ll be using in this series is the JHD12864E. Here’s a picture of what it looks like (image stolen from http://extremeelectronics.co.in):
It’s a fairly standard 128×64 pixels display with a backlight. The part number aside, what really matters is the IC driver that is used in this display. The datasheet shows (more on this in a few mins) that it uses the S6B0108 display driver. After looking around on the net, I realised that this is similar to the KS0108 family display driver. So the general method of operation should be similar to the KS0108 but with a few minor differences here and there. Continue reading
This is going to be a mini-series on how to get started with a 128×64 LCD display. I’ll be going through all the steps that are involved in getting one of these damned things to work and I’ll post links and references wherever necessary.
“But”, you argue, “why do I need to learn this stuff? I can just whip out my Arduino and use the GLCD library and be just as cool!” Well, definitely. The purpose of doing this is not to be “cool”, but to gain an understanding into how this works and what kinds of problems you may face when working on something like this.
I won’t go too much into the pros and cons of which is a better approach. Obviously, libraries are there for a reason and if you’re using a specific development platform/board (Arduino, EasyPic) or a specific compiler for a certain project (AVR-GCC, MikroC, XC8) and you’re on a deadline and have a fairly straightforward task to accomplish, you should go ahead with that.
On the other hand, if LCD.Write(“Hello, World!”) doesn’t cut it anymore and you want to have complete control on a pixel to pixel basis, and/or be able to churn out your own library for a specific microcontroller that you’re currently using (8051, PIC, AVR, MSP) then you should read these series of posts.
On the whole, I will try to keep this series largely microcontroller agnostic. You should be able to read whatever is given here and transfer the learning to any microcontroller or development platform with a small amount of effort.
But for the sake of demonstration, I will be using a PIC16F886 microcontroller here. I have used both AVR and PIC and they’re both excellent microcontrollers in terms of performance, price and availability. But I’m going with a PIC here because I’m trying to learn more about these microcontrollers.
Here’s the table of contents. I will keep updating the links as I push content out:
- Intro – Getting started with a 128×64 Graphics LCD Display
- Part 1 – Getting started with a 128×64 Graphics LCD Display – JHD12864E (KS0108 family)
- Part 2 – Getting started with a 128×64 Graphics LCD Display – Screen resolution and locating pixels
- Part 3 – Getting started with a 128×64 Graphics LCD Display – Passing instructions
- Part 4 – Getting started with a 128×64 Graphics LCD Display – Pin configuration
- Part 5 – Getting started with a 128×64 Graphics LCD Display – Putting it together
- Part 6 – Getting started with a 128×64 Graphics LCD Display – Hello World!
- Part 7 – Getting started with a 128×64 Graphics LCD Display – Porting a bitmap to the GLCD
- Part 8 – Getting started with a 128×64 Graphics LCD Display – Fonts! Fonts! Fonts!
- Part 9 – Getting started with a 128×64 Graphics LCD Display – Pitfalls, debugging and troubleshooting