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Microcontroller with LCD interface applications introduced
2011-09-06 by seoer

Liquid crystal display (LCD) with low voltage, micropower, informative display and convenient interface, etc., has now been widely used in computers and digital instrumentation in areas such as measurement results and an important tool for man-machine dialogue. LCD display can be divided into three categories according to their functions: pen-stage liquid crystal display, the character dot matrix liquid crystal display and dot matrix LCD display. The first two can display numbers, characters and symbols, and graphic dot matrix LCD can display characters and any graphics, to the effect of illustrations, and its more widely.

GTG240128 LCD module:

1 Module Features

GTG240128 dot matrix dot matrix LCD display size of 240 × 128, with a backlight function. Built a T6963C LCD controller and five KS0086 drive. The LCD module has the following characteristics.

● 8-bit parallel bus interface, can be directly connected with the 80 series of microprocessors;

● You can display numbers, letters, characters and graphics;

● has 128 kinds of ASCI 5 × 8 dot character font libraries CGROM;

● The display has a 64kb memory (can be divided into text display, graphic display, text and custom character property for the reservoir area), and allows the MCU to access at any time;

● available graphical, text and graphics and text display synthesis.

2 Module Interface Pin Function

GTG240128 liquid crystal display module and a microprocessor interface 21-pin, the pin functions shown in Table 1.

3 Module Instruction Set Introduction

GTG240128 LCD module uses the hardware initialization settings, making it the command functions concentrated in the display settings, thereby enhancing the display capabilities. The module command with one or two parameters, or may not take parameters. If the command contains a parameter, it must be entered before the command. Data or instructions in each write operation and data read operations should be carried out before testing the status word, not only in the "busy" state, MCU with a module to be effective. The status bits of meaning from low to high as shown in Table 2.

The MCU to write instructions or a read / write data, S0 and S1 to the same time effectively; when the MCU using the automatic read / write function, S2 and S3 will replace the S0 and S1 as a busy flag, then MCU will determine whether it effective; S6 is to investigate the T6963C screen reading or screen copy command implementation flag; S5 and S7 modules that run within the state, generally do not.

The interface circuit with AT89C55

GTG240128 AT89C55 interface with direct access and indirect access in two ways. Direct access method is to display the module as a memory or I / O devices directly linked to the microcontroller bus; indirect access method is to display module with a microcontroller I / O interface, the microcontroller through the I / O port operation of indirect to achieve control of the module. In this paper, direct access, the hardware to connect the circuit shown in Figure 1.

LCD module data lines connected to the AT89C55 the data bus, chip select signals from address lines A7 and A0 to provide the register select signal from the address lines A7 and A1 provide (command channel address 0xf1, data channel address 0xf3), read and write operations by the signal control read and write AT89C55; module Vo end of the potentiometer connected to adjust the graphics LCD display contrast.

Software Design

Software using Keil C51 language development, including three parts: the first is a write command and write data for the liquid crystal display module hardware drivers; second part consists of liquid crystal display module to initialize and clear screens generic subprogram; The third part is the characters, character and graphics display program.

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