Working with Shift Registers and a PIC help - Page 5 - Electronic Circuits Projects Diagrams Free

Darkstar64 · 3rd October 2008, 10:43 PM

wow ive spent all day on this how hard can it be to make this work

here is my code. I want it to read the 8 bit string and then one digit after the other send it out on pin GP0 and then after each digit it needs to clock on GP1 the one im using needs a low to high to clock it please help ive been at this for days I don't know if the engine works or not ether please haha I only want the first 4 LED's to light up on the shift hence the '11110000'

Code:

    list      p=12F509            ; list directive to define processor
    #include <p12F509.inc>        ; processor specific variable definitions

    __CONFIG   _MCLRE_ON & _CP_OFF & _WDT_OFF & _IntRC_OSC

; '__CONFIG' directive is used to embed configuration word within .asm file.
; The lables following the directive are located in the respective .inc file. 
; See respective data sheet for additional information on configuration word.



	cblock	0x07
;***** VARIABLE DEFINITIONS
count,temp
D
CP
delay
	endc




;**********************************************************************
RESET_VECTOR    CODE   0x3FF      ; processor reset vector

; Internal RC calibration value is placed at location 0x3FF by Microchip
; as a movlw k, where the k is a literal value.
    
MAIN    CODE    0x000
    movwf   OSCCAL            ; update register with factory cal value 


start
		movlw	b'11110000'
		movlw	temp
		call	shift
		goto	start
;********Subroutines********
shift
shift5	movlw	0x08		;set loop counter
		movwf	count
		movf	INDF,w		;get a byte
		movwf	temp
shift1	        rrf	temp,f		;rotate ms-bit into carry
		btfsc	STATUS,C	;is it 0?
		goto	shift2		;no, shift out a 1
		goto	shift3		;yes, shift out a 0
shift2	        bsf	GPIO,1
		nop
		bsf	GPIO,1		;blip clock
		nop
		bcf	GPIO,1
		goto	shift4
shift3	        bcf	GPIO,1
		nop
		bsf	GPIO,1		;blip clock
		nop
		bcf	GPIO,1
shift4	        decfsz	count,f		;done 8-bits?
		goto	shift1		;no, go again
               retlw 0
		
		END					; End of program !!

[/CODE]

futz · 4th October 2008, 01:01 AM

Quote:

Originally Posted by Darkstar64

wow ive spent all day on this how hard can it be to make this work

here is my code.

I see two things right off the bat:

1. You haven't set your pins to outputs with TRIS. By default, PIC pins are inputs on reset. To make them outputs you must set them yourself.

2. You're using the same pin for both data and clock. That won't work.

Here's your code neatened up and decluttered (so I could read it comfortably). I did not make the fixes listed above. You can do that.

You don't need to mess around with that reset vector thing or the osc calibration value. I removed that stuff.

Code:

	#include <P12F509.inc>
	__CONFIG _MCLRE_ON & _WDT_OFF & _IntRC_OSC

	cblock	0x07
	count,temp
	endc

	org	0x000
main	movlw	b'11110000'
	movlw	temp
	call	shift5
	goto	main

shift5	movlw	0x08		;set loop counter
	movwf	count
	movf	INDF,w		;get a byte
	movwf	temp
shift1	rrf	temp,f		;rotate ms-bit into carry
	btfsc	STATUS,C	;is it 0?
	goto	shift2		;no, shift out a 1
	goto	shift3		;yes, shift out a 0
shift2	bsf	GPIO,1
	nop
	bsf	GPIO,1		;blip clock
	nop
	bcf	GPIO,1
	goto	shift4
shift3	bcf	GPIO,1
	nop
	bsf	GPIO,1		;blip clock
	nop
	bcf	GPIO,1
shift4	decfsz	count,f		;done 8-bits?
	goto	shift1		;no, go again
	retlw 0
		
	end

Darkstar64 · 4th October 2008, 05:27 AM

ok so it would look something like this then o and about the tris I had that done in another part I deleted just forgot to put it back in I guess . I changed the pins is this correct and I added the tris part its just not shown is that everything?

Code:

	#include <P12F509.inc>
	__CONFIG _MCLRE_ON & _WDT_OFF & _IntRC_OSC

	cblock	0x07
	count,temp
	endc

	org	0x000
main	movlw	b'11110000'
	movlw	temp
	call	shift5
	goto	main

shift5	movlw	0x08		;set loop counter
	movwf	count
	movf	INDF,w		;get a byte
	movwf	temp
shift1	rrf	temp,f		;rotate ms-bit into carry
	btfsc	STATUS,C	;is it 0?
	goto	shift2		;no, shift out a 1
	goto	shift3		;yes, shift out a 0
shift2	bsf	GPIO,1
	nop
	bsf	GPIO,2		;blip clock
	nop
	bcf	GPIO,2
	goto	shift4
shift3	bcf	GPIO,1
	nop
	bsf	GPIO,2		;blip clock
	nop
	bcf	GPIO,2
shift4	decfsz	count,f		;done 8-bits?
	goto	shift1		;no, go again
	retlw 0
		
	end

futz · 4th October 2008, 05:54 AM

Quote:

Originally Posted by Darkstar64

ok so it would look something like this then o and about the tris I had that done in another part I deleted just forgot to put it back in I guess . I changed the pins is this correct and I added the tris part its just not shown is that everything?

If you're going to use GPIO2 as an output then you must clear T0CS in the OPTION register (I put the tris line in too) or it just won't work:

Code:

	movlw	b'11001000'	;clear T0CS for output on GPIO2
	option
	movlw	b'00001000'	;set pins to all outs
	tris	GPIO

Alternately, you could probably use

Code:

	bcf	OPTION,T0CS

I haven't tested that line though. Would have to have a look in the datasheet to see if I had some reason for doing all 8 bits there.

futz · 4th October 2008, 06:20 AM

Cube page on my site (link below) has been updated. There's a YouTube video of it working too.

Darkstar64 · 4th October 2008, 08:04 PM

Ok well thanks alot all give that a try now when I write this code it should only lite up the first 4 LED's right and they will stay on just making sure bc its been doing some weird stuff with some of code ive givin it thanks alot for the help all let you know how it goes

Darkstar64 · 4th October 2008, 08:36 PM

Ok it just doesn't want to work no matter what I try I am hooking up the Data and Shift right into the PIC on pins GP1 and GP2 can you post a schmatic I could try with my MC74HC595A shift register and some assembler just to test to make sure its working I have tried everything I can shift it manually but when I hook it into the pic nothing happens or something happens just not what I told it to do here is the code I have programmed in it would help if you could give me a small simple test schmatic that I could use I have one but its for manually shifting the register. I don't think ive ever had so much problems with one thing it just won't work I don't get it

skyhawk · 4th October 2008, 08:51 PM

I don't have time to study your code in detail, but are you latching your output?

futz · 4th October 2008, 08:56 PM

Quote:

Originally Posted by Darkstar64

Ok it just doesn't want to work no matter what I try I am hooking up the Data and Shift right into the PIC on pins GP1 and GP2 can you post a schmatic I could try with my MC74HC595A shift register and some assembler just to test to make sure its working I have tried everything I can shift it manually but when I hook it into the pic nothing happens

Then you're doing it wrong.

My schematic wouldn't help you much. I'm using totally different parts.

Show me your schematic and your code! Then I (and/or others) can probably spot the problem. A photo is sometimes helpful too. Camera set on macro with a steady hand and LOTS of light.

I could maybe even breadboard up the identical thing for better troubleshooting.

Darkstar64 · 4th October 2008, 08:58 PM

No im not but its doing it by itself for some unknown reason I don't even have a connection hooked up to it so all try addding a wire to GP4 to latch it it says a low to high will latch it so all test it out fast and tell you what happens ok so my final code is here with the latch at the very bottom is this correct ? and when I post the code into here it comes out weird its not like that in MPLAB

Code:

	#include <P12F509.inc>
	__CONFIG _MCLRE_ON & _WDT_OFF & _IntRC_OSC

	cblock	0x07
	count,temp
	endc

		org	0x000
main	movlw	b'11001000'	;clear T0CS for output on GPIO2
		option
		movlw	b'00001000'	;set pins to all outs
		tris	GPIO
		movlw	b'11110000'
		movlw	temp
		call	shift5
		goto	main

shift5	movlw	0x08		;set loop counter
		movwf	count
		movf	INDF,w		;get a byte
		movwf	temp
shift1	rrf	temp,f		;rotate ms-bit into carry
		btfsc	STATUS,C	;is it 0?
		goto	shift2		;no, shift out a 1
		goto	shift3		;yes, shift out a 0
shift2	bsf	GPIO,1
		nop
		bsf	GPIO,2		;blip clock
		nop
		bcf	GPIO,2
		goto	shift4
shift3	bcf	GPIO,1
		nop
		bsf	GPIO,2		;blip clock
		nop
		bcf	GPIO,2
shift4	decfsz	count,f		;done 8-bits?
		goto	shift1		;no, go again
		bcf		GPIO,4
		bsf		GPIO,4
		retlw 0
		
	end

futz · 4th October 2008, 09:03 PM

Quote:

Originally Posted by skyhawk

I don't have time to study your code in detail, but are you latching your output?

That sounds right. Darkstar's code was NOT latching.

Darkstar, the reason my code has no latching is because the shift register I use auto-latches. The leading 1 is pushed into the latch by the 36th bit shifted. A 74HC595 must be manually latched.

futz · 4th October 2008, 09:05 PM

Quote:

Originally Posted by Darkstar64

No im not but its doing it by itself for some unknown reason I don't even have a connection hooked up to it

It may be floating and just kinda sometimes latching by itself.

Put a NOP between those two, or you may have a problem.

Code:

	bcf		GPIO,4
	bsf		GPIO,4
	retlw 0
		
	end

Darkstar64 · 4th October 2008, 09:06 PM

Ya at the bottom of my code is the latching now just before retlw 0 but it still doesn't want to work haha

Darkstar64 · 4th October 2008, 09:09 PM

Ok it seems to be working but the LED's are wrong for some reason here is what it is happening '10011000' instead of the '11110000'

skyhawk · 4th October 2008, 09:10 PM

Back to basics. Why not put a 1 on the output pin, clock it, latch it, and test whether the first output pin on the shift register is high.

edit: Disregard. I see it's working.

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4th October 2008, 06:20 AM	#65
futz	Cube page on my site (link below) has been updated. There's a YouTube video of it working too. __________________ ========================= Futz's Microcontrollers & Robotics =========================

4th October 2008, 08:04 PM	#66
Darkstar64	Ok well thanks alot all give that a try now when I write this code it should only lite up the first 4 LED's right and they will stay on just making sure bc its been doing some weird stuff with some of code ive givin it thanks alot for the help all let you know how it goes

4th October 2008, 08:36 PM	#67
Darkstar64	Ok it just doesn't want to work no matter what I try I am hooking up the Data and Shift right into the PIC on pins GP1 and GP2 can you post a schmatic I could try with my MC74HC595A shift register and some assembler just to test to make sure its working I have tried everything I can shift it manually but when I hook it into the pic nothing happens or something happens just not what I told it to do here is the code I have programmed in it would help if you could give me a small simple test schmatic that I could use I have one but its for manually shifting the register. I don't think ive ever had so much problems with one thing it just won't work I don't get it Last edited by Darkstar64; 4th October 2008 at 08:53 PM.

4th October 2008, 08:51 PM	#68
skyhawk	I don't have time to study your code in detail, but are you latching your output?

4th October 2008, 09:06 PM	#73
Darkstar64	Ya at the bottom of my code is the latching now just before retlw 0 but it still doesn't want to work haha

4th October 2008, 09:09 PM	#74
Darkstar64	Ok it seems to be working but the LED's are wrong for some reason here is what it is happening '10011000' instead of the '11110000'

4th October 2008, 09:10 PM	#75
skyhawk	Back to basics. Why not put a 1 on the output pin, clock it, latch it, and test whether the first output pin on the shift register is high. edit: Disregard. I see it's working. Last edited by skyhawk; 4th October 2008 at 09:12 PM.