# Part 2 – Getting started with a 128×64 Graphics LCD Display – Screen resolution and locating pixels

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.

But each column (of 64 pixels) is broken down into 8 pages or segments of 1 byte each. Let’s spend a moment here and it’s even worth repeating – Each column is broken down into 8 pages of 1 byte each. This means each column has 8 bytes which equals 64 bits. Depending on whether the bit in each of the 8 bytes is HIGH(1) or LOW (0), the corresponding pixel is toggled on or off. The pages are addressed using the X address which ranges from 0 to 7.

Here is the most important point – In every instruction to display data on the screen, we pass one byte of information which tells which pixel to turn on and which one to turn off at the specified Y and X position.

So effectively, this requires four separate sequences of instructions:

1. Specify which half to use
4. Specify which pixels to turn on and off through one byte of data

The diagram below gives an overview of how the screen is broken down: In the next part we’ll cover how the instructions are sent to the display

1. alperen
• voidcast