74HC164 Shift Register Doubt - Electronic Circuits Projects Diagrams Free

Gayan Soyza · 17th February 2009, 04:24 AM

I have been fine tuning my 5(columns) X 7(rows) matrix system using 74HC164.
But still I'm not getting a smooth display result.I'm doubt with the "Clock_Pulse" routine.

Code:

Do_Show		call	Reset		;reset 74HC
		bsf	Data		;make 74HC data pin high for the first time
		movf	Col1,W
		call	Clock_Pulse
		bcf	Data		;make 74HC data pin low 
		movf	Col2,W
		call	Clock_Pulse
		movf	Col3,W
		call	Clock_Pulse
		movf	Col4,W
		call	Clock_Pulse
		movf	Col5,W
		call	Clock_Pulse
		goto	Do_Show	


Clock_Pulse	movwf	Col_Data	;get the column data
		clrf	PORTB						
		bsf	Clock		;low to high transition
		bcf	Clock		;make low for next transition
		movf	Col_Data,W
		movwf	PORTB														
		return

arhi · 17th February 2009, 04:37 AM

add a single nop between bsf and bcf

Code:

..
		bsf	Clock		;low to high transition
                nop                          ;give shift register time to act
		bcf	Clock		;make low for next transition
...

depending on the clock of your uC and the type of the shift register you might add more then one nop (note that HC is few times slower then HCT especially if you are running it on 3V - if you are using 5V rails only - use HCT .. much faster)

arhi · 17th February 2009, 04:42 AM

I just checked the DS, the min time for the pulse is 5ns so one nop is enough

Gayan Soyza · 17th February 2009, 04:44 AM

Hi arhi thanks for you help.

Crystal is 4Mhz.Supply is 5V.
The letter is displaying but I can see an additional column.Also I can see the off state LEDs also lights very dimly.

I have put an 4.7K pullup resister to the reset pin of 74HC.I think that also better if I can remove and connect that reset pin to direct to PIC.

arhi · 17th February 2009, 04:52 AM

the HC is fast enough for what you need but in general, HCT is faster

not that it would make many difference .. you need that nop for the clock ...

now, that's what you need to change in the pulse sub ... as for the whole code .. it looks ok ... try with the nop and say if it is ok now

Gayan Soyza · 17th February 2009, 04:56 AM

Earlier I did my Reset routine like this with tristate condition.

Code:

Reset		bsf	STATUS,RP0
		bcf	TRISA,2		;make RA2 output
		bcf	STATUS,RP0
		;
		bcf	PORTA,2		;reset pulse
		nop			;//
		nop			;//
		bsf	STATUS,RP0
		bsf	TRISA,2		;;make RA2 input
		bcf	STATUS,RP0
		return

After calling this "Reset" Routine that 4.7K pullup resister will hold the reset pin of 74HC high.I don't know why I did like that stupid.

arhi · 17th February 2009, 05:07 AM

IIRC reset pin is active low, so if you push up with 10K (or 4.7K, I prefere 10K) and do what you did it should work ... but .. why would you do it ? if you are reserving a pin for reset pin, you do not need to pull-up .. just connect to pic, bcf reset; nop, nop, bsf reset ... and go forward

Gayan Soyza · 17th February 2009, 05:11 AM

I totally agree with you arhi

I'll try with the adjustments & tell the latest progress.

be80be · 17th February 2009, 05:46 AM

I found what I used to get mine to work

Code:

Dataout macro Var,Var1
	Local 	Loop
	movlw	.8
	movwf	Var1
Loop  rlf	Var,f
	btfss	STATUS,C
	bcf	Data
	btfsc	STATUS,C
	bsf	Data
	bsf	Clock
	nop
	nop
	nop
	nop
	bcf	Clock
	decfsz 	Var1,f
	goto	Loop
	endm

which it the same s arhi I added some nop to get a good clock

be80be · 17th February 2009, 05:51 AM

I have change my shift registers 74hc595n it has a latch thay work alot better and only 19cents each

arhi · 17th February 2009, 05:52 AM

latch is nice but requires extra pin

Gayan Soyza · 17th February 2009, 07:05 AM

HI be80be thanks for your contribute.

By looking at your code can you tell are you feeding the row data via a shift register or direct from PORTB?

be80be · 17th February 2009, 02:37 PM

here this shows better the macro sends the data out and this shows how it is loaded

Code:

Main					;main program

	movlw	0x07
	movwf	CMCON			;turn comparators off (make it like a 16F84)
	banksel TRISA
	movlw	b'00011000'		;initializing porta
	movwf	TRISA
	banksel	PORTA
	clrf 	PORTA
Send
	movlw 	b'00000001'			;fill tx buffer
	movwf	TX
	HC4015 TX,CountSPI
	goto	Send1
Send1
	movlw 	b'00000010'			;fill tx buffer
	movwf	TX
	HC4015 TX,CountSPI
	goto	Send2
Send2
	movlw 	b'00000100'			;fill tx buffer
	movwf	TX
	HC4015 TX,CountSPI
	goto	Send3
Send3
	movlw 	b'00001000'			;fill tx buffer
	movwf	TX
	HC4015 TX,CountSPI
	goto Send4
Send4
	movlw 	b'00010000'			;fill tx buffer
	movwf	TX
	HC4015 TX,CountSPI
	goto Send5
Send5
	movlw 	b'00010000'			;fill tx buffer
	movwf	TX
	HC4015 TX,CountSPI
	goto	Send6
Send6
	movlw 	b'00100000'			;fill tx buffer
	movwf	TX
	HC4015 TX,CountSPI
	goto	Send7
Send7
	movlw 	b'01000000'			;fill tx buffer
	movwf	TX
	HC4015 TX,CountSPI
	goto Send8
Send8
	movlw 	b'10000000'			;fill tx buffer
	movwf	TX
	HC4015 TX,CountSPI
	goto Send		
Loop

Gayan Soyza · 18th February 2009, 02:57 AM

Hi Arhi I solved my clock pulse routine.You must waste cycles after clearing the PORTB.
Also I added that nop as well

Code:

;**********************************
;Clock pulse routine to SR-74HC164
;**********************************

Clock_Pulse	movwf	Col_Data	;save column data
		clrf	PORTB
		goto	$+1
		goto	$+1
		goto	$+1
		goto	$+1
		goto	$+1												
		bsf	PORTA,0		;low to high transition
		nop				
		bcf	PORTA,0		;make low for next transition
		nop
		movf	Col_Data,W
		movwf	PORTB	
		goto	$+1
		goto	$+1
		return

Gayan Soyza · 18th February 2009, 03:01 AM

Now a serious problem I'm having.I spent many hours to solve my new problem but I couldn't do that.

I can scroll a letter from right to left slowly.When I make it speed scrolling it displays like mirroring.Not smooth lines moving.

I have put a new thread regarding this for assistance.

Led Matrix Mirroring Problem.

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17th February 2009, 04:37 AM	#2
arhi	add a single nop between bsf and bcf Code: .. bsf Clock ;low to high transition nop ;give shift register time to act bcf Clock ;make low for next transition ... depending on the clock of your uC and the type of the shift register you might add more then one nop (note that HC is few times slower then HCT especially if you are running it on 3V - if you are using 5V rails only - use HCT .. much faster)

17th February 2009, 04:42 AM	#3
arhi	I just checked the DS, the min time for the pulse is 5ns so one nop is enough

17th February 2009, 04:44 AM	#4
Gayan Soyza	Hi arhi thanks for you help. Crystal is 4Mhz.Supply is 5V. The letter is displaying but I can see an additional column.Also I can see the off state LEDs also lights very dimly. I have put an 4.7K pullup resister to the reset pin of 74HC.I think that also better if I can remove and connect that reset pin to direct to PIC. __________________ Gayan My Website http://gsmicro.blogspot.com/

17th February 2009, 04:52 AM	#5
arhi	the HC is fast enough for what you need but in general, HCT is faster not that it would make many difference .. you need that nop for the clock ... now, that's what you need to change in the pulse sub ... as for the whole code .. it looks ok ... try with the nop and say if it is ok now

17th February 2009, 04:56 AM	#6
Gayan Soyza	Earlier I did my Reset routine like this with tristate condition. Code: Reset bsf STATUS,RP0 bcf TRISA,2 ;make RA2 output bcf STATUS,RP0 ; bcf PORTA,2 ;reset pulse nop ;// nop ;// bsf STATUS,RP0 bsf TRISA,2 ;;make RA2 input bcf STATUS,RP0 return After calling this "Reset" Routine that 4.7K pullup resister will hold the reset pin of 74HC high.I don't know why I did like that stupid. __________________ Gayan My Website http://gsmicro.blogspot.com/ Last edited by Gayan Soyza; 17th February 2009 at 04:57 AM.

17th February 2009, 05:07 AM	#7
arhi	IIRC reset pin is active low, so if you push up with 10K (or 4.7K, I prefere 10K) and do what you did it should work ... but .. why would you do it ? if you are reserving a pin for reset pin, you do not need to pull-up .. just connect to pic, bcf reset; nop, nop, bsf reset ... and go forward

17th February 2009, 05:11 AM	#8
Gayan Soyza	I totally agree with you arhi I'll try with the adjustments & tell the latest progress. __________________ Gayan My Website http://gsmicro.blogspot.com/

17th February 2009, 05:46 AM	#9
be80be	I found what I used to get mine to work Code: Dataout macro Var,Var1 Local Loop movlw .8 movwf Var1 Loop rlf Var,f btfss STATUS,C bcf Data btfsc STATUS,C bsf Data bsf Clock nop nop nop nop bcf Clock decfsz Var1,f goto Loop endm which it the same s arhi I added some nop to get a good clock

17th February 2009, 05:51 AM	#10
be80be	I have change my shift registers 74hc595n it has a latch thay work alot better and only 19cents each

17th February 2009, 05:52 AM	#11
arhi	latch is nice but requires extra pin

17th February 2009, 07:05 AM	#12
Gayan Soyza	HI be80be thanks for your contribute. By looking at your code can you tell are you feeding the row data via a shift register or direct from PORTB? __________________ Gayan My Website http://gsmicro.blogspot.com/ Last edited by Gayan Soyza; 17th February 2009 at 07:06 AM.

18th February 2009, 03:01 AM	#15
Gayan Soyza	Now a serious problem I'm having.I spent many hours to solve my new problem but I couldn't do that. I can scroll a letter from right to left slowly.When I make it speed scrolling it displays like mirroring.Not smooth lines moving. I have put a new thread regarding this for assistance. Led Matrix Mirroring Problem. __________________ Gayan My Website http://gsmicro.blogspot.com/ Last edited by Gayan Soyza; 18th February 2009 at 03:31 AM.