Lesson 23: LED Nixie Tube Static Display Interface and Programming

In single chip microcomputer system, led nixie tube display is often used to display various numbers or symbols. Because it has the characteristics of clear display, high brightness, low voltage and long service life, it is widely used.

Introduction: remember the "matchstick game" we played when we were children? Several matchsticks can be combined to form a variety of graphics. In fact, led nixie tube display is such a thing.

Eight Segment LED nixie tube display

The eight Segment LED nixie tube display is composed of eight light-emitting diodes. In the base, seven long strip-shaped light-emitting tubes are arranged in the shape of "day". Another dot shaped light-emitting tube is used to display the decimal point in the lower right corner of the nixie tube display. It can display various numbers and some English letters. Led nixie tube display has two different forms: one is that the anodes of 8 light-emitting diodes are connected together, which is called common anode led nixie tube display; The other is that the cathodes of 8 light-emitting diodes are connected together, which is called common cathode led nixie tube display. As shown in the figure below

The name and arrangement position of each stroke segment of LED nixie tube display with common Yin and common Yang structure are the same. When the diode is turned on, the corresponding stroke segments are illuminated, and various characters are displayed by the combination of the illuminated stroke segments. Eight stroke segments hgfedcba correspond to D7 D6 D5 D4 D3 D2 D1 d0 of one byte (8 bits), so the font code of the character to be displayed can be represented by an 8-bit binary code. For example, for the common cathode led nixie tube display, when the common cathode is grounded (zero level) and the anode hgfedcba sections are 011011, the nixie tube display displays the "P" character, that is, for the common cathode led nixie tube display, the font code of the "P" character is 73h. If it is a common anode led nixie tube display, the common anode is connected to high level, and the font code of "P" character shall be 10001100 (8CH). It must be noted here that in order to facilitate wiring, many products often do not correspond to the relationship between fields and bits in a regular way. At this time, the font code must be designed according to the wiring. We will give a routine later.

In the application system of single chip microcomputer, there are two common methods for nixie tube display: static display and dynamic scanning display. The so-called static display means that each nixie tube display occupies a separate I / O interface with latch function for stroke segment font code. In this way, as long as the single chip microcomputer sends the font code to be displayed to the interface circuit, it doesn't have to worry about it. Until new data is to be displayed, it will send a new font code. Therefore, using this method, the CPU overhead in the single chip microcomputer is small. There are many I / O interface circuits that can provide separate latch. Here, taking the commonly used serial parallel conversion circuit 74LS164 as an example, a commonly used static display circuit is introduced to make everyone have a certain understanding of static display.

The serial port mode of MCS-51 single chip microcomputer is shift register mode, 6 pieces of 74LS164 are connected externally as the static display interface of 6-bit led nixie tube display, RXD of 8031 is used as the data output line and TXD is used as the shift clock pulse. 74LS164 is a TTL unidirectional 8-bit shift register, which can realize serial input and parallel output. Among them, a and B (pins 1 and 2) are serial data input terminals. The two pins input signals according to the logic and operation law. When one input signal is common, it can be connected in parallel. T (pin 8) is the clock input terminal, which can be connected to the TXD terminal of the serial port. When the rising edge of each clock signal is added to the t end, the shift register is moved by one bit. After 8 clock pulses, all 8-bit binary numbers are moved into 74LS164. R (pin 9) is the reset end. When r = 0, each bit of the shift register is reset to 0. Only when r = 1, the clock pulse works. The parallel output terminals of Q1... Q8 (pins 3-6 and 10-13) are respectively connected to the corresponding pins of hg--- a segments of LED nixie tube display. The 74LS164 can also be introduced as follows: the so-called clock pulse end actually requires high, low, high and low pulses. No matter how the pulse comes, for example, we use a wire, one end is connected to t, the other end is held by hand, and the high level and low level are connected respectively. That is to give the clock pulse and obtain the clock pulse at the moment of 74LS164 (to be clear, it is at the edge of the pulse) if the data input terminal (pins 1 and 2) If it is a high level, a 1 will enter the 74LS164. If the data input is a low level, a 0 will enter the 74LS164. After eight pulses are given, the first data entering the 74LS164 reaches the highest level, and then what happens to another pulse? Another pulse, the first pulse will move out of the highest level, just like the station platoon When the team buys tickets, the railing is so long. If you want to go in from the back, you must go out from the front.

After understanding this point, let's look at the circuit. Six pieces of 7ls164 are connected in series, and the clock ends are connected together. In this way, when eight pulses are input, the data output from the RXD end of the single chip microcomputer enters the first piece of 74LS164. When the second eight pulses arrive, the data enters the second piece of 74LS164, and the new data enters the first piece of 74LS164. In this way, When the sixth eight pulses are completed, the data sent for the first time is sent to the leftmost 164, and other data appears in the first, second, third, fourth and fifth 74LS164 in turn. There is a problem. When the first pulse arrives, what are the other chips doing except receiving data in the first 74LS164? They are also receiving data, because their clock ends are connected together Yes, but the data has not been sent to other chips yet. What data are they receiving? In fact, the so-called data is just a statement. In fact, it is the level. When the first pulse arrives, the first chip 164 certainly receives data from the single chip microcomputer, and other chips are also connected to the Q8 of the previous chip, which is a wire, which is used in the digital circuit There are only two possible states: low or high, i.e. "0" and "1" So its next 74LS164 is also receiving data. It only receives 0 or 1. This problem is explained here. Some friends may ignore it, but some friends may still not know it. This actually involves the essence of numbers. If you don't understand it, please think carefully, find some numbers of digital circuits and understand the working principle of 164, Let's look at this problem again, or take a look at my other article "lesson 27: some basic concepts about single chip microcomputer". Be sure to understand it. If you understand this, your level will be higher than the beginning learner and can be described as a beginner.

Entry: put the number to be displayed in 6 units of display buffer 60h-65h respectively, and correspond to each nixie tube led0-led5 respectively.

Exit: convert the 6 numbers preset in the display buffer into corresponding display font codes, and then output them to the nixie tube display for display.

The LED display program of single chip microcomputer is as follows:

Disp: mov scon, #00h; initialize serial port mode 0

Mov R1, #06h; display 6 digits

Mov R0, #65h; 60h-65h is the display buffer

Mov dptr, #segtab; entry address of font table

LOOP:

Mov a, @ R0; take the highest data to be displayed

MOVC a, @ a dptr; look up the table to get the font code

Mov SBUF, a; send serial port display

Delay: JNB Ti, delay; wait for sending

CLR Ti; clear send flag

Dec R0; the pointer moves down one bit, ready to take down a number to be displayed

Djnz R1, loop; until all 6 data are displayed.

RET

Settab: font table, which was introduced earlier. We will introduce the production of font table later.

DB 03H 9FH 27H 0DH 99H 49H 41H 1FH 01H 09H 0FFH

; 0 1 2 3 4 5 6 7 8 9 blanking code

Main program for single chip microcomputer display test

ORG 0000H

AJMP START

ORG 30H

START: MOV SP,#6FH

MOV 65H,#0

MOV 64H,#1

MOV 63H,#2

MOV 62H,#3

MOV 61H,#4

MOV 60H,#5

LCALL DISP

SJMP $

If the nixie tube is arranged as shown in the figure, the above main program will display 543210. Think about it. How to send data if 012345 is to be displayed?

Next, let's analyze the making of font table. Let's look at the above "standard" graphics first. Write the corresponding relationship between data bits and font and make a table as follows (set it as common Yang type, that is, when the corresponding output bit is 0, the pen segment is bright)

How about the font table? Just make a table like this. Write the 0 and 1 of the corresponding bits according to the requirements (0 or 1). Do an exercise and write the font code of a-f.

If the order of wiring is disrupted for the convenience of wiring, how to connect the font table? It is also very simple and the same list. Take the new experimental board as an example, common Yang type. The wiring is as follows:

P0.7 P0.6 P0.5 P0.4 P0.3 P0.2 P0.1 P0.0

C E H D G F A B

Then the font code is as follows:

;0 00101000 28H

;1 01111110 7EH

;2 10100100 0A4H

;3 01100100 64H

;4 01110010 72H

;5 01100001 61H

;6 00100001 21H

;7 01111100 7CH

;8 00100000 20H

;9 01100000 60H

As an exercise, write the font code of a-f.

Originally, this is to explain the static interface of single-chip microcomputer nixie tube display. This should be the end, but I also want to talk about the essence of numbers mentioned above. There are some terms and nouns in single-chip microcomputer that originally help us understand things, but sometimes we will be confused by the related semantics of these terms, so that we can't further understand their essence Therefore, we are generally confused. Only by deeply understanding the working characteristics of 74LS164 can we really understand what serial data is. Interested friends can also look at my website to find relevant content

Lesson 23: LED Nixie Tube Static Display Interface and Programming 1

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