Design of LCD display control circuit based on AT89S52

1 AT89S52 MCU Introduction

1.1 Main features of the chip

The AT89S52 microcontroller is a high-end, enhanced product recently launched by Atmel. It is a low-power, high-performance CMOS 8-bit microcontroller, with a general-purpose 8-bit central processor and ISP FLASH storage unit, 8 kB ISP (In-system programmable) FLASH read-only program memory that can be repeatedly erased and written 1,000 times. The on-chip FLASH allows the program memory to be programmable in the system and is also suitable for conventional programmers. The device is manufactured using Atmel's high-density, non-volatile storage technology, compatible with the standard MCS-51 instruction system and 80C51 pin structure. On a single chip, it has a smart 8-bit CPU and in-system programmable FLASH, making the AT89S52 a highly flexible and cost-effective solution for many embedded control application systems.

1. 2 AT89S52 pin arrangement

The AT89S52 microcontroller has three packaging types: PDIP, PLCC and TQFP (see Figure 1 for the common PDIP arrangement).

Figure 1 AT89S52 MCU pin arrangement

2 DMC20261 LCD display

The DMC20261 LCD module consists of three parts:

LCD controller, driver, and display. See Figure 2.

Figure 2 LCD internal structure diagram

At present, most LCD monitors use an integrated controller model HD44780. HD44780 is a controller and driver integrated circuit dedicated to character display control and driving.

HD44780 is a representative circuit of character LCD display controller. Its main features are:

HD44780 is not only a controller but also has the ability to drive 40 @ 16 dot matrix LCD pixels, and the driving capability can be expanded to 360 columns through an external driver; the display buffer and user-defined character generator CGRAM are all built-in; it has an interface suitable for the M6800 series MPU, and the interface data transmission can be 8-bit data and 4-bit data transmission in two ways; it has a simple but powerful instruction set, which can realize display functions such as character movement and flashing (see Table 1); due to the limited DDRAM capacity of HD44780, the characters that HD44780 can control are up to 80 words per line, that is, 5 @ 80 = 400 points, and it has 16 row drivers and 40 column drivers, so HD44780 itself has the ability to drive 16 @ 40 dot matrix LCD (that is, 16 characters in a single line and 8 characters in 2 lines); the built-in character generation memory (CGROM) 160 different dot matrix character graphics have been stored (see Figure 3), for example, the code for the number / 10 is 00110001B (31H), and the code for the capital letter / A0 is 01000001B (41H).

2.1 LCD controller instructions

There are 11 commands for character LCD, and their detailed functions and usage are shown in Table 1.

Table 1 LCD instruction table

2.2 Character graphic code

Character graphic code (as shown in Figure 3).

Figure 3. Correspondence table of CGROM and CGRAM character graphics codes of LCD display

3 Design of LCD and AT89S52 interface

3.1 Hardware circuit design

In actual applications, there are many ways to connect LCD modules to single-chip microcomputers. There are serial and parallel modes based on the number of I/O port lines occupied. The serial mode is slower and occupies fewer I/O ports. The parallel mode is divided into 4-wire and 8-wire, faster and occupies more I/O ports. In actual applications, the parallel mode is the most common. At present, the 51 series single-chip microcomputer is the most widely used type at home and abroad. The following introduces the interface circuit designed by the author for your reference. [page]

The connection circuit between some pins of the microcontroller's P0 and P3 ports and the DMC20261 LCD display is shown in Figure 4.

Figure 4 LCD display and control circuit

3.2 Software Design

A simple display program is written based on the DMC20261 character graphic code and the instruction characteristics of the controller / Huaian Vocational College 0. Among them, P35 is the command/character, P36 is read/write, P37 is the pulse pin, and P0 port is the data terminal. Each Chinese character occupies 5 columns and 8 rows of dot matrix, and two rows can program up to 16 characters. The main program flow chart is shown in Figure 5. The program written and debugged successfully using the adjustment software Dev C + + IDE is attached later.

Figure 5 Main program flow chart

Note: * indicates it can be 0 or 1.

The control system utilities are as follows: