Working with Shift Registers and a PIC help - Page 3 - Electronic Circuits Projects Diagrams Free

skyhawk · 8th September 2008, 06:24 PM

Quote:

However, you are not completely correct on your description of the 12 bit chips. On the 509 you can make calls to addresses in the 0x200-0x2ff region by setting the PA0 bit in status. You can also use the two pages that are not accessible to calls for tables as computed gotos will still work.

I thought I covered the bases with:

Quote:

These PICs have the instruction space divided into 512 word pages. Only the first 256 words of a page can be used as the destination of a subroutine call or instruction that modifies PCL. In addition, care must be taken that the page select bits in the STATUS register are set for a GOTO, CALL, or instruction that modifies the PCL.

Total memory space 1024 words, 512 word pages, so need to set page select bit (PA0) in STATUS register to access all of memory.

I'm not sure how you do a computed GOTO, but I do it by doing arithmetic on PCL to select the GOTO in a table of GOTOs, since that modifies PCL then the table of GOTOs must be in the first 256 words of each page. In that case I have used space in that area for GOTO's rather than data tables. I don't see the gain. Using GOTO's will allow one to move the body of a subroutine out of the top half of the page as long as the entry point is there.

My point was/is that one can do tricks to get around the limitations of baseline PICs, but that is something that is probably beyond the skills/understanding of a beginner.

Mike you are most geneous with the help you give beginners here on the forum.

Pommie · 9th September 2008, 02:44 AM

Sorry Skyhawk, I didn't see your earlier post and was responding to your post immediately above mine. You are also correct on the computed gotos, I didn't realise the call bug also effected writes to PCL.

Mike.

futz · 10th September 2008, 03:18 AM

Well Mr. Darkstar, I got myself a couple 12F509's and some HEF4894B 12-stage shift registers in my Digikey order today. We shall see how well this crappy little chip can drive a 3x3x3 LED cube.

The 12F509 took me some time to get used to. Took me an hour or two to figure out the chip's strange quirks and get an LED flashing on GPIO2. Now that I have the chip's oddities figured out I can move on. What a bare-bones chip!

My blinky prog:

Code:

	include	"P12F509.INC"
	__config _IntRC_OSC & _WDT_OFF & _MCLRE_ON

	cblock	0x07
	d1,d2
	endc

	org	0x000
init	movlw	b'11001000'	;clear T0CS for output on GPIO2
	option
	movlw	b'001000'	;set pins to all outs
	tris	GPIO
	clrf	GPIO		;zero all pins
main	bsf	GPIO,2
	call	delay
	bcf	GPIO,2
	call	delay
	goto	main

delay	movlw	0x3e		;0.2 second delay
	movwf	d1
	movlw	0x50
	movwf	d2
delay_0	decfsz	d1, f
	goto	del1
	decfsz	d2, f
del1	goto	delay_0
	retlw	0

	end

futz · 11th September 2008, 06:19 AM

Quote:

Originally Posted by futz

and some HEF4894B 12-stage shift registers in my Digikey order today. We shall see how well this crappy little chip can drive a 3x3x3 LED cube.

Aaarrrggghhh! My LED cube is common cathode, but my new shift registers are open drain, so I need a common anode cube! Oh well, I guess I'm building a new cube. Think I'll go 4x4x4 (for other MCUs) and red LEDs this time.

I can only use 3x3x3 of it with the 12F509 due to too few pins (509 has 5 outs). Need 2 pins to control the shift register and 3 for the anodes. Hmm... I guess I could add another shift register to control the anodes and would only need 4 output pins that way... And I could go to a 8x8x8 cube!

(I'd probably run out of memory on this tiny chip though.)

Pommie · 11th September 2008, 06:28 AM

Why not just cascade two (or more) shift registers.

Mike.

futz · 11th September 2008, 06:32 AM

Quote:

Originally Posted by Pommie

Why not just cascade two (or more) shift registers.

That had crossed my mind too. You're talking about controlling cathodes and anodes off a couple or three cascaded shift registers, right?

Pommie · 11th September 2008, 06:55 AM

Yes, you could drive the anodes via high side PNPs. So 4*4 is 16 cathodes plus 4 anodes can fit on two 12 bit shift registers.

Mike.

futz · 11th September 2008, 07:10 AM

Quote:

Originally Posted by Pommie

Yes, you could drive the anodes via high side PNPs. So 4*4 is 16 cathodes plus 4 anodes can fit on two 12 bit shift registers.

Groovy!

It shall be done! Might have to solder together a control board. It gets very hectic wiring that much stuff on a breadboard. I'll just socket the PIC so I can replace it with a 12F683 later when I run out of space (and patience) with the 12F509. No interrupts! Ridiculous!

Pommie · 11th September 2008, 07:47 AM

I think you'll find the 2 level deep stack to be very constricting. And you'll miss things like addlw.

Mike.

**Nigel Goodwin** · 11th September 2008, 09:12 AM

Quote:

Originally Posted by Pommie

I think you'll find the 2 level deep stack to be very constricting. And you'll miss things like addlw.

Yes, it's ludicrous bodging lot's of extra hardware on because you're using too small a device, plus the 12 bit PIC's are very limited compared with the 14 bit ones, never mind the 16 bit ones.

In the distant past you had no choice if you wanted a tiny PIC, but for many years now you have been able to get 14 bit PIC's in 8 pin packages, even including A2D.

futz · 13th September 2008, 07:13 AM

Quote:

Originally Posted by Pommie

Yes, you could drive the anodes via high side PNPs. So 4*4 is 16 cathodes plus 4 anodes can fit on two 12 bit shift registers.

Here is where my electronics noobishness comes in.

I understand (kinda) how to do a high side PNP switch, but what transistor can switch 320mA (16 LEDs @ 20mA)? Or should I be looking at MOSFET's or maybe Darlington arrays?

**Nigel Goodwin** · 13th September 2008, 09:13 AM

Quote:

Originally Posted by futz

I understand (kinda) how to do a high side PNP switch, but what transistor can switch 320mA (16 LEDs @ 20mA)?

Almost all transistors can switch 320mA (only the very smallest can't) - it's not a very difficult power level.

Try a BC327 at 800mA.

Mike, K8LH · 13th September 2008, 10:22 AM

Quote:

Originally Posted by futz

Here is where my electronics noobishness comes in.

I understand (kinda) how to do a high side PNP switch, but what transistor can switch 320mA (16 LEDs @ 20mA)? Or should I be looking at MOSFET's or maybe Darlington arrays?

2N4403 (PNP, Fairchild, 600 ma), TO-92 or SOT23
PN2907A (PNP, Fairchild, 800 ma), TO-92 or SOT23

FDN304PZ (P-FET, Fairchild, 2.4a, Rds(on) = 0.052 ohms), SOT23

MIC2981 (eight 500 ma high side sourcing drivers), PDIP or SOIC

futz · 13th September 2008, 04:25 PM

Thanks Nigel and Mike.

All I have in stock is 2N3906. Guess I'll cook up another order and get some more parts.

futz · 16th September 2008, 04:00 AM

Ha! Better yet, I had a look at one of the MM5451YN chips I recently bought just to see what they were about. Perfect! It's a 35-bit shift register with open-drain drivers for LEDs. Send a 1 as your first bit of 36 and it auto-latches when all 36 bits have been clocked in - so it only needs 2 pins, clock and data. Reasonable price too.

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9th September 2008, 02:44 AM	#32
Pommie	Sorry Skyhawk, I didn't see your earlier post and was responding to your post immediately above mine. You are also correct on the computed gotos, I didn't realise the call bug also effected writes to PCL. Mike.

10th September 2008, 03:18 AM	#33
futz	Well Mr. Darkstar, I got myself a couple 12F509's and some HEF4894B 12-stage shift registers in my Digikey order today. We shall see how well this crappy little chip can drive a 3x3x3 LED cube. The 12F509 took me some time to get used to. Took me an hour or two to figure out the chip's strange quirks and get an LED flashing on GPIO2. Now that I have the chip's oddities figured out I can move on. What a bare-bones chip! My blinky prog: Code: include "P12F509.INC" __config _IntRC_OSC & _WDT_OFF & _MCLRE_ON cblock 0x07 d1,d2 endc org 0x000 init movlw b'11001000' ;clear T0CS for output on GPIO2 option movlw b'001000' ;set pins to all outs tris GPIO clrf GPIO ;zero all pins main bsf GPIO,2 call delay bcf GPIO,2 call delay goto main delay movlw 0x3e ;0.2 second delay movwf d1 movlw 0x50 movwf d2 delay_0 decfsz d1, f goto del1 decfsz d2, f del1 goto delay_0 retlw 0 end __________________ ========================= Futz's Microcontrollers & Robotics ========================= Last edited by futz; 11th September 2008 at 04:55 AM.

11th September 2008, 06:28 AM	#35
Pommie	Why not just cascade two (or more) shift registers. Mike.

11th September 2008, 06:55 AM	#37
Pommie	Yes, you could drive the anodes via high side PNPs. So 4*4 is 16 cathodes plus 4 anodes can fit on two 12 bit shift registers. Mike.

11th September 2008, 07:47 AM	#39
Pommie	I think you'll find the 2 level deep stack to be very constricting. And you'll miss things like addlw. Mike.

13th September 2008, 04:25 PM	#44
futz	Thanks Nigel and Mike. All I have in stock is 2N3906. Guess I'll cook up another order and get some more parts. __________________ ========================= Futz's Microcontrollers & Robotics =========================

16th September 2008, 04:00 AM	#45
futz	Ha! Better yet, I had a look at one of the MM5451YN chips I recently bought just to see what they were about. Perfect! It's a 35-bit shift register with open-drain drivers for LEDs. Send a 1 as your first bit of 36 and it auto-latches when all 36 bits have been clocked in - so it only needs 2 pins, clock and data. Reasonable price too. __________________ ========================= Futz's Microcontrollers & Robotics =========================