New to shift registers

[Andrew Cowan]

I'm working my way around shift registers, and learning how to use them.

I'm just wondering - is there an easier way to code this:
pulsout 1,1
pulsout 2,1 '(clock)
pulsout 1,1
pulsout 2,1 '(clock)
pulsout 2,1 '(clock)
pulsout 2,1 '(clock)
pulsout 3,1 '(latch)

Thanks,

Andrew

 

[westaust55]

Andrew,

from looking at your past posts looks like you have a 28X.
So you do need to bit bash the byte out one bit at a time - which what I believe you are trying to do.

In simple terms, you need to
1. identify if the bit to be sent is a 1 or 0
2. set up the output data pin to suit (as 1 or 0)
3. pulse the clock pin (while the data is steady)
4. shift the data in PICAXE to lok at next bit
5, goto 1 (above) until required number of bits are sent.
6. pulse the latch pin to move data within shift register to the shift register outputs.

Suggest have a look at Dr Acula's thread here:
http://www.picaxeforum.co.uk/showthread.php?t=9116&highlight=595*

 

[Andrew Cowan]

Thanks westaust55. Although I do not need this for any current project, I'm just experimenting. Currently I have connected the shift register to an 08M. The Programming and customizing the Picaxe Microcontroller book has a good tutorial on shift registers.

Your post said I would have to bit bang if I use a 28X - are there other chips (eg 28X1) that don't need bit banging? What do you do with these?

Thanks,

Andrew

 

[westaust55]

With the X1 parts (28X1 and 40X1), the SHIFTOUT command can be used.

Here is a sample of the code that is then used:

; test program to drive 8 LED via a 74HC595
; program uses the shiftout command instead of pushing bits out one at a time
; lit LED starts at the LSB (right) side and steps to the MSB (left) side
; then steps back again to the LSB side. Continues back and forth forever . . .

symbol clock = 4           ; clock on Output 4
symbol serdata = 5        ; data output on Output 5
symbol latch = 6           ; latch to 595 outputs with high pulse on Output 6
symbol bitz = 8             ; number of bits to send
symbol msb_1st = 1       ; 1 = MSB first and idle state is low
symbol pattern = b20     ; variable to hold the LED pattern
symbol delaytime = b21  ; delay between 'stepping' to next LED pattern

init: low latch
      low clock
      pattern = %00000001
      delaytime = 500    ; 500 = 0.5 sec for slow step rate. At 20 if "flies"

main:
	DO
		GOSUB out_595
		pause delaytime
		pattern = pattern <<1
	loop until pattern=%10000000
	DO
		GOSUB out_595
		pause delaytime
		pattern = pattern >>1
	loop until pattern=%00000001
	goto main

out_595:
	shiftout clock,serdata,msb_1st,(pattern/bitz)
	pulsout latch,5
	return

 

[hippy]

In terms of 'easiest' and 'best' ways to code control of shift registers it frequently depends upon what the criteria is; fastest code where program memory used isn't a problem, smallest code where speed isn't that important.

The X1's offer SHIFTOUT which is both fast and compact. For others, bit-banging can be done in a FOR-NEXT loop ( slow but compact ) or 'unrolled' so it's a sequence of set and pulse commands ( faster but more code ).

The X1's also have HSPIOUT which is even faster than SHIFTOUT but requires certain I/O pins to be used. Bit-banging techniques can still be used on the X1's if that's prefered.

 

[Andrew Cowan]

Thanks - I'll let you know how I get on. I think I will start by counting with a seven segment display via an 08M.

Andrew