Simulator Software
Basic Serial - Shift register
7 Segment
Clock While Data Input High
Turn off Screen
Reset
Integrated Circuit Packages
Common Cathode / Anode
Automate Display Function

Published February 1, 2024 © GPL3+

Shift Register Hands On

Imagine doing this by hand. Now you can simulate the experience! Follow along with discreet components.

IntermediateProtip2 hours446

Things used in this project

Hardware components

Texas Instruments Shift Register- Serial to Parallel

7 Segment LED Display, InfoVue

Resistor 100 ohm

Breadboard (generic)

Software apps and online services

SimulIDE simulator program

Story

It takes 9 leads to connect one of these 7 segment display modules. Multiplexing and other techniques allow us to use fewer wires and interface larger displays. This project use a chip called the shift register.

Simulator Software

You can build this circuit with discreet components. I am using a simulator software called SimulIDEthat has an example circuit named shiftregister-test.sim1 located in Logic/Arithmetic examples. There are other quality simulators available.

The gray squares are voltage on/off switches to our chip leads. Simulide will do a safety shutdown when you make changes to circuit hardware or software. Click on them. Simulation On/Off power at the top of the screen.

Basic Serial - Shift register

Toggle the clock input and apply 5v to the DI data input. With each on/off clock cycle the voltage you put in is passed down the shift register pins from Q0 to Q7. Rst clears the stored bits.

7 Segment

Remove the round lamps and add a 7 segment LED with the a through g and dot connections. Simulide will do a safety shutdown when you make changes to circuit hardware or software.

Clock While Data Input High

Hold DI data input at 5v for 8 clock cycles and we fill the screen. All 7 segments and the dot light up. After we stop inputting voltage blanks will cycle through.

Turn off Screen

We can blank the display between characters. Toggle the OE output enable lead on the shift register chip while there is a byte. Notice shift register outputs shut down and the bits stay in their buffer.

Reset

We start fresh. Toggle the reset lead and we clear the byte that was in the shift register circuit.

Integrated Circuit Packages

Wouldn't it be nice for our shift register to hold the current byte of LED segments while loading a new 8 bits? We call that a latch or buffer. It can be built in the chip with the shift register or it can be an added module.

Look at this package containing a shift-register with latch and LEDs combined. Here is a circuit from a 4pin serial display module. See how it includes the shift register we've been studying?

Think of the latch as a second clock that toggles every 8 bits so that bytes have starts and finishes. Often latch is unused. Data comes in on SDI serial data input. Trace how output Q7 has a SDO serial data output lead so that the MSB bit can rollover to another shift register, like the carry operation in addition.

If you want to do a simulator hands-on with this device it is located in SimulIDE data files led_display\1bit_led_sca.sim1. How to make connections in basic SimulIDE project. Look at specs for 4 pin serial 7 segment LED display modules.

In 2x4bit_led_cc.sim1 we see Q7 from the first shift register roll over to a second. Q7 of the second shift register rolls over to the DO data output pin of the 4pin package.

Common Cathode / Anode

We picked a circuit where the LED current goes to ground. We apply positive voltage to each segment to light them. This means our software will need to generate ones. We call this Common Cathode.

Common Anode is wired the opposite way. The LED module has a +ve lead and we apply voltage for blank and ground to light.

Automate Display Function

Now that we know how to move bits through these circuits let us put a computer to work on it. We build this circuit in our Assembly project.

We will use this connection table. Notice how the names change?

Here is the Uno version. Same thing but different.

hc595_mega328.asm

Assembly x86

SimulIDE has a simulation with an ATmega328 connected to a 74hc595 shift register with a 7segment LED display. Compiled hex file shifts a bit from Q0->Q7 to light up bars and dot on display.

Arduino connections to 74hc595
portb.1 pin9 DS data
portb.2 pin10 OE output enable
portb.3 pin11 STC clock
portb.4 pin12 SHC latch
portb.5 pin13 MR reset

Files are in folder \SimulIDE\examples\Micro\Avr\mega328\m328_hc595\gcb_code\
hc595_mega328.asm - compiles with both Avra and Microchip assemblers
hc595_mega328.gcb - Great Cow Basic
provides accurate values for SER OE RCLK SRCLK SRCLR
portb.1 portb.2 portb.3 portb.4 portb.5
74hc595.gcb - Great Cow Basic incomplete, no comments, no pin numbers

Erratum!: the simulation uses leds to show bit shifting from Q0->Q7 apologies

; hc595_mega328.asm from Simulide Arduino with 595 shift register LEDs
;  cycles a to g segments and dot 
;  from \SimulIDE\examples\Micro\Avr\mega328\m328_hc595\gcb_code\
;   file hc595_mega328.asm   compiles with avra and microchip 
;Chip Model: MEGA328P
;Assembler header file
.INCLUDE "m328pdef.inc"

;SREG bit names (for AVR Assembler compatibility, GCBASIC uses different names)
#define I 7
#define T 6
#define H 5
#define S 4
#define V 3
#define N 2
#define Z 1
#define C 0

;********************************************************************************

;Set aside memory locations for variables
.EQU	BITOUT=256
.EQU	INDEX=257

;********************************************************************************

;Register variables
.DEF	DELAYTEMP=r25
.DEF	DELAYTEMP2=r26
.DEF	SysBitTest=r5
.DEF	SysCalcTempA=r22
.DEF	SysValueCopy=r21
.DEF	SysWaitTempMS=r29
.DEF	SysWaitTempMS_H=r30
.DEF	SysTemp1=r0

;********************************************************************************

;Vectors
;Interrupt vectors
	nop
	rjmp	BASPROGRAMSTART ;Reset
	nop
	reti	;INT0
	nop
	reti	;INT1
	nop
	reti	;PCINT0
	nop
	reti	;PCINT1
	nop
	reti	;PCINT2
	nop
	reti	;WDT
	nop
	reti	;TIMER2_COMPA
	nop
	reti	;TIMER2_COMPB
	nop
	reti	;TIMER2_OVF
	nop
	reti	;TIMER1_CAPT
	nop
	reti	;TIMER1_COMPA
	nop
	reti	;TIMER1_COMPB
	nop
	reti	;TIMER1_OVF
	nop
	reti	;TIMER0_COMPA
	nop
	reti	;TIMER0_COMPB
	nop
	reti	;TIMER0_OVF
	nop
	reti	;SPI_STC
	nop
	reti	;USART_RX
	nop
	reti	;USART_UDRE
	nop
	reti	;USART_TX
	nop
	reti	;ADC
	nop
	reti	;EE_READY
	nop
	reti	;ANALOG_COMP
	nop
	reti	;TWI
	nop
	reti	;SPM_READY

;********************************************************************************

;Start of program memory page 0
nop
BASPROGRAMSTART:
;Initialise stack
	ldi	SysValueCopy,high(RAMEND)
	out	SPH, SysValueCopy
	ldi	SysValueCopy,low(RAMEND)
	out	SPL, SysValueCopy
;Call initialisation routines
	rcall	INITSYS

;Start of the main program
	rcall	INIT595
SysDoLoop_S1:
	ldi	SysValueCopy,1
	sts	BITOUT,SysValueCopy
	rcall	SHIFTBIT
	ldi	SysWaitTempMS,244
	ldi	SysWaitTempMS_H,1
	rcall	Delay_MS
	ldi	SysValueCopy,0
	sts	INDEX,SysValueCopy
SysForLoop1:
	lds	SysTemp1,INDEX
	inc	SysTemp1
	sts	INDEX,SysTemp1
	ldi	SysValueCopy,0
	sts	BITOUT,SysValueCopy
	rcall	SHIFTBIT
	ldi	SysWaitTempMS,244
	ldi	SysWaitTempMS_H,1
	rcall	Delay_MS
	lds	SysCalcTempA,INDEX
	cpi	SysCalcTempA,7
	brlo	SysForLoop1
SysForLoopEnd1:
	rjmp	SysDoLoop_S1
SysDoLoop_E1:
BASPROGRAMEND:
	sleep
	rjmp	BASPROGRAMEND

;********************************************************************************

Delay_MS:
	inc	SysWaitTempMS_H
DMS_START:
	ldi	DELAYTEMP2,254
DMS_OUTER:
	ldi	DELAYTEMP,20
DMS_INNER:
	dec	DELAYTEMP
	brne	DMS_INNER
	dec	DELAYTEMP2
	brne	DMS_OUTER
	dec	SysWaitTempMS
	brne	DMS_START
	dec	SysWaitTempMS_H
	brne	DMS_START
	ret

;********************************************************************************

INIT595:
	sbi	DDRB,5
	sbi	DDRB,4
	sbi	DDRB,3
	sbi	DDRB,2
	sbi	DDRB,1
	cbi	PORTB,5
	cbi	PORTB,4
	cbi	PORTB,3
	cbi	PORTB,2
	cbi	PORTB,1
	sbi	PORTB,5
	ret

;********************************************************************************

INITSYS:
	ldi	SysValueCopy,0
	out	PORTB,SysValueCopy
	ldi	SysValueCopy,0
	out	PORTC,SysValueCopy
	ldi	SysValueCopy,0
	out	PORTD,SysValueCopy
	ret

;********************************************************************************

SHIFTBIT:
	cbi	PORTB,3
	cbi	PORTB,4
	cbi	PORTB,1
	lds	SysBitTest,BITOUT
	sbrc	SysBitTest,0
	sbi	PORTB,1
	sbi	PORTB,4
	sbi	PORTB,3
	ret

;********************************************************************************

hc595_mega328.gcb

Plain text

// sample program hc595_mega328.gcb from 
//  \SimulIDE\examples\Micro\Avr\mega328\m328_hc595\gcb_code\hc595_mega328.gcb
// the example does shift bit Q0->Q7 to drive 7 segment + dot
// the example hex file may be compiled from hc595_mega328.asm
// 
#chip mega328P, 16

#include "74hc595.gcb"

#define SER     portb.1
#define OE      portb.2
#define RCLK    portb.3
#define SRCLK   portb.4
#define SRCLR   portb.5

init595
do
    shiftBit( 1 )
    wait 500 ms
    
    for index=1 to 7
        shiftBit( 0 )
        wait 500 ms
    next
loop

74hc595.gcb

Plain text

'#define SER
'#define OE
'#define RCLK
'#define SRCLK
'#define SRCLR

'#define delay595

#define clear595 SRCLR = 0

Sub init595
    Dir SRCLR   out
    Dir SRCLK   out
    Dir RCLK    out
    Dir OE      out
    Dir SER     out
    SRCLR = 0           'Clear shiht register
    SRCLK = 0           '
    RCLK  = 0           '
    OE    = 0           'Enable outputs
    SER   = 0
    
    SRCLR = 1
End Sub  

Sub shiftByte( in byteout as byte )    'LSB first
    RCLK = 0
    for num=0 to 7
        SRCLK = 0
        SER   = byteout.0
        SRCLK = 1
        rotate byteout right
        #ifdef delay595
        wait delay595 
        #endif
    next
    RCLK = 1
End Sub

Sub shiftBit( in bitout as bit )
    RCLK  = 0
    SRCLK = 0
    SER   = bitout.0
    SRCLK = 1
    RCLK  = 1
End Sub

Characters on 7 segment LED display
***********************************
case 0: 1, 1, 1, 1, 1, 1, 0, 0
case 1: 0, 1, 1, 0, 0, 0, 0, 0
case 2: 1, 1, 0, 1, 1, 0, 1, 0
case 3: 1, 1, 1, 1, 0, 0, 1, 0
case 4: 0, 1, 1, 0, 0, 1, 1, 0
case 5: 1, 0, 1, 1, 0, 1, 1, 0
case 6: 1, 0, 1, 1, 1, 1, 1, 0
case 7: 1, 1, 1, 0, 0, 0, 0, 0
case 8: 1, 1, 1, 1, 1, 1, 1, 0
case 9: 1, 1, 1, 1, 0, 1, 1, 0

case 'a': 1, 1, 1, 0, 1, 1, 1, 0
case 'b': 0, 0, 1, 1, 1, 1, 1, 0
case 'c': 1, 0, 0, 1, 1, 1, 0, 0
case 'd': 0, 1, 1, 1, 1, 0, 1, 0
case 'e': 1, 0, 0, 1, 1, 1, 1, 0
case 'f': 1, 0, 0, 0, 1, 1, 1, 0
case 'h': 0, 1, 1, 0, 1, 1, 1, 0
case 'l': 0, 0, 0, 1, 1, 1, 0, 0
case 'p': 1, 1, 0, 0, 1, 1, 1, 0
case 'q': 1, 1, 1, 0, 0, 1, 1, 0
case 'u': 0, 1, 1, 1, 1, 1, 0, 0
case 'y': 0, 1, 1, 1, 0, 1, 1, 0
***********************************
try adding decimal point for more characters

Credits

Patrick Fitzgerald

124 projects • 51 followers

Shift Register Hands On

Things used in this project

Hardware components

Software apps and online services

Story

Simulator Software

Basic Serial - Shift register

7 Segment

Clock While Data Input High

Turn off Screen

Reset

Integrated Circuit Packages

Common Cathode / Anode

Automate Display Function

Code

hc595_mega328.asm

hc595_mega328.gcb

74hc595.gcb

LEDtable.txt

Credits

Patrick Fitzgerald

Comments

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Shift Register Hands On

Shift Register Hands On

Things used in this project

Hardware components

Software apps and online services

Story

Simulator Software

Basic Serial - Shift register

7 Segment

Clock While Data Input High

Turn off Screen

Reset

Integrated Circuit Packages

Common Cathode / Anode

Automate Display Function

Code

hc595_mega328.asm

hc595_mega328.gcb

74hc595.gcb

LEDtable.txt

Credits

Patrick Fitzgerald

Comments

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