Serial-In/Parallel-Out Shift Registers...

Forum 2005-2010 (read only) Hardware Interfacing
#1

Sorry if this has been answered before; I did a decent amount of searching but couldn't quite find the info I'm after.

My understanding of serial->parallel shift register ICs is that you have to bring CLK high for every bit in the transmission? I was wondering if I could use the serial TX on a Duemilanove to control one, but am a bit stuck working out what to use as a clock pulse and how to keep it in sync with the serial transmission.

Hoping someone can point me in the right direction here.

Cheers.

#2

any reason why?

cause there is a shift out function that takes care of most of that for you

#3

but am a bit stuck working out what to use as a clock pulse and how to keep it in sync with the serial transmission.

Can you explain a little more what it is you want to do? Problem with using the serial line to clock out data is that the serial line doesn't have a transition for every data bit - if you were to transmit an 0x20 (space), vs a 0x5A ('Z'), the number of edges does not equal the number of bits (in either case).

#4

Wow that was easy. :smiley:

I didn’t know that facility was already in the system! Cheers Osgeld, much appreciated mate.

I think I might put my project ideas on hold and just work through all the available Arduino tutorials. There’s clearly so much in there that I don’t know exists.

#5

Problem with using the serial line to clock out data is that the serial line doesn't have a transition for every data bit - if you were to transmit an 0x20 (space), vs a 0x5A ('Z'), the number of edges does not equal the number of bits (in either case).

That's the kind of thing I was worried about... but it looks like the shiftOut() func and tutorial (found those quite easy once I knew they existed) will be what I'm after.

Just experimenting with some off-board RAM and CPU chips but they all require more pins that I can afford to use. Might buy a Mega some day.

#6

what kind of SR are you using? (yea you said s<>p but theres a few different models)

#7

None as yet - was going to head out to Maplin/RS tomorrow and pick something up; but wanted to get things straight in my head on how to do all this before I went.

#8

Check the difference in price of the 74HC595 and HEF4795

The HEF chip is geared towards LED driving and can drive a bit more power. You can use a pwm pin on the enable output to dim the LEDs on one or more chips.

I need to try the G pin on the 595 with pwm and see if that causes dimming.

#9