Hardware exploration -- Design and manufacture of digital clock

One 、 The experiment purpose ：

Design one with 60 Into the system and 24 Hexadecimal counting function , Clock circuit that can correct time and display through decoder and seven segment nixie tube .

Functional requirements ： Triggered by continuous pulses , second 、 It is divided into 60 Decimal count , When is 24 Decimal count , And require decoding 、 Show 、 Timing .

Two 、 Design steps

1） The chips used 2-5-10 Decimal counter （74LS90）, Draw the pin diagram 、 Menu .

74LS90 Pin diagram

 

 74LS90 Menu

Input						Output				function
clear 0		Set up 9		The clock		QD	QC	QB	QA
R01	R02	S91	S92	1CP	2CP
1	1	0	X	X	X	0	0	0	0	clear 0
		X	0
0	X	1	1	X	X	1	0	0	1	Set up 9
X	0
0        X X        0		0        X X        0		↓	1	QA Output				Binary count
				1	↓	QDQCQB Output				Pental count
				↓	QA	QDQCQBQA Output 8421BCD code				Decimal count

 2） Designed to have 24 Base number 、60 It's binary Count 、 decoding 、 Circuit diagram shown （24 Base number 、60 Binary circuit diagram ）

60 Decimal count 、 decoding 、 Display circuit

 

24 Decimal count 、 decoding 、 Display circuit

 

3） Explain the working principle of the design circuit .（ How to realize sub circuit Count 、 Base number , How to carry one bit to ten ？）

1、60 The working principle of binary circuit

This circuit is the second counting circuit of digital clock , It uses two 74LS90N Counting chip , Accept the input of clock pulse , Both the one bit and ten bit counters are set to 10 Decimal counter , The carry signal of bits is used as the clock input signal of the ten bit counter .

When the bit count reaches 9 when , And gate output high level , The next cycle bit will be cleared , And gate produces a falling edge , At this time, the ten digit counter is incremented by one , Complete a carry from one bit to ten bits .

When the ten digit count reaches 6 when , The ten bit counter will be reset through the feedback of the gate circuit , At the same time, a carry signal is generated and provided to the next bit , To achieve 60 Binary count .

2、24 The working principle of binary circuit

The circuit is an hour counting circuit of digital clock , It uses two 74LS90N Counting chip , Accept the carry pulse input of the minute counting circuit , Both bits and tens are set to 10 Decimal counter , The carry signal of bits is used as the clock input signal of the ten bit counter .

When the bit count reaches 9 when , And gate output high level , The next cycle bit will be cleared , And gate produces a falling edge , At this time, the ten digit counter is incremented by one , Complete a carry from one bit to ten bits .

When the ten digit count reaches 2 And the bit count reaches 3 when （ namely 23 when ）, The one bit and ten bit counters will be cleared at the same time through the feedback of the gate circuit , To achieve 24 Decimal count .

Draw 6 position Count 、 decoding 、 Display the overall diagram of the circuit .---24 Hour timing

General circuit diagram

 

1、 Explain the working principle of the whole diagram .

a、 Second counting circuit 、 The sub counting circuits are 60 Binary design , Ten are 6 Base number , Bits are 10 Base number , When the ten reached 5 when , A carry signal and a clear signal are generated through the gate circuit , On the falling edge of the next clock , Zero the ten bits and carry them back , Complete a carry process .

b、 The circuit passes through 6 A dial switch is connected to 6 Clock signal input of counters , Use a button to manually generate a clock signal , Each bit can be controlled individually , If necessary, you can also disconnect the clock input terminal of the second signal , Accurate timing of the circuit including seconds .