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Understanding shift registers — Parallax Forums

Understanding shift registers

OakGraphicsOakGraphics Posts: 202
edited 2009-11-21 16:00 in Accessories
Howdy Gang,

I have felt inspired by watching Ben Heck's pinball building from scratch with a propeller chip and thought it would be good for me to understand the various ways he is using the input/output of shift registers to increase his I/O for the propeller. I know he uses the 74x595 for output and the 4021 series for the input but I have never seen a 4021 with cascade logic like you can do with the 595's. Looking at the specs from www.classiccmp.org/rtellason/chipdata/bu4021b.pdf I have not been able to figure out how to 'cascade' read several chips. Any help would be appreciated. smile.gif

Comments

  • OakGraphicsOakGraphics Posts: 202
    edited 2009-11-17 06:03
    I like answering my own posts. smile.gif

    I found this site that kinda details what I was thinking it was doing:
    arcadecontrols.com/arcade_sneskey.html
    quench_SNESPAD.GIF
    I kinda felt the Q8 was what you connect to the next in line. I assume the Q6 Q7 Q8 were done to allow different counting styles?
  • kwinnkwinn Posts: 8,697
    edited 2009-11-20 22:56
    Pin 11 is the serial data input and pin 3 is the serial output. Connect them together and parallel pins 9 and 10 and you have a 16 bit shift register. The signal on pin 9 will load the parallel data into the chips and the clock on pin 10 will shift all 16 bits.
  • ElectricAyeElectricAye Posts: 4,561
    edited 2009-11-21 05:10
    OakGraphics said...
    I like answering my own posts. smile.gif



    You're welcome.

    tongue.gif
  • kwinnkwinn Posts: 8,697
    edited 2009-11-21 16:00
    FYI, I believe the '4021 is obsolete. I had a hard time sourcing it a while back and switched to the 74HC595. It is the functional but not pin/signal equivalent.
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