Keywords: MM5483, LCD display, serial interface
1 Introduction?
Because of its excellent characteristics such as low voltage, low power consumption, and direct drive with CMOS circuits, liquid crystal display has been widely used in various fields. Liquid crystal display devices can be divided into two major categories: dot matrix type and segment type on display pixels. The dot matrix LCD screen can generally display more complicated graphics or characters, but its interface is also more complicated and the cost is relatively high. In many industrial intelligent display instrument applications, segment-type liquid crystal display can meet the needs. Because of this, segmented LCDs still have a wide application market.
MM5483 is a serial interface produced by National Semiconductor Corporation (that is, NaTIonal Semiconductor, see http://TIonal.com/) and can drive a 31-segment low-power LCD driver. Its cascadable features allow it to be flexibly configured to suit more complex display occasions.
2 MM5483 chip description?
2.1 MM5483 internal block diagram?
The internal interface block diagram of MM5483 is shown in Figure 1. It interfaces with the CPU through 3 pins: 22 pin is the input pin of serial display data bit; 21 pin is the shift pulse input end of serial data, the rising edge moves the serial data into; 25 pin is Register data latch pulse input terminal, the high level will move into the data output in the register. In addition, 18 pins are used to display the cascade of the chip; 19 pins are the input of the working pulse of the chip; 23 pins are the back pole output pins; 24 pins are the back pole input pins; 1, 20 pins are the chip Power supply terminal; the rest are 31 LCD drive segment code output pins.
2.2 MM5483 interface mode There are two ways of interface between MM5483 and CPU, namely 3-wire and 2-wire.
The 3-wire interface control mode circuit is shown in Figure 2. In this interface mode, the display operation can be divided into two steps: first, the shift input of the display data bit; when all the data is moved into the display register, it is then output to the LCD screen at once. In this interface mode, when the data to be displayed is moved, it does not affect the current data display, but it requires three CPU I / O interface lines.
The sequential logic of the 3-wire interface control mode is shown in Figure 3. First, output the data bits to be displayed to the DATA INPUT terminal, and use the rising edge of the CLOCK terminal to shift the data into the display register. After all the data is moved in, a high level is generated at the LOAD terminal to latch the data and output it to the LCD screen.
The 2-wire control interface circuit is shown in Figure 4. In this way, the LOAD terminals of all MM5483 can be directly connected to the high level, which can save another I / O line. In this way, every time a data bit to be displayed is moved, the data of the display register is directly output to the LCD screen. Judging from the effect of refreshing the display, it is not as good as the previous interface method. Because when the display data is refreshed, if the data transfer speed is low, you will see that the data is "walking" bit by bit on the LCD screen. The sequential logic of the data movement is completely consistent with the 3-wire control method.
3 MM5483 display programming implementation The following uses the LCD display driver of the computer fueling machine as an example to introduce the preparation of the display driver in the 3-wire interface mode. This program is written in the extended C language supported by the Keil C51 compiler and debugged on Keil C 6.20 (Keil Software's product, see http: //.com/). 
4 Conclusion This chip has a wide operating voltage range and can be adapted to system applications with 3.0V to 10.0V power supply. The working temperature of the chip is in the range of 45 ℃ ～ + 85 ℃. The anti-riot test of the fuel tanker and various electromagnetic tests and the field application of the tax-controlled tanker show that the MM5483 has high anti-interference performance, and has high stability and reliability.
references
1 Li Wei, edited by Guo Qiang. Liquid crystal display application technology. Beijing: Electronic Industry Press, 2000
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