shift register 101

[keny]

Hey there, I am trying to ask this in a non-redundant been asked a thousand times way, but I am trying to get the scoop on the following setup:

Pic 18 (any) -> 74H164 (serial in / parallel out shift register)

I guess I am looking for an explanation of two methods:

Bit Banging method

USart Method

My questions are:

1. If I send the MCU's internal Clock straight to the shift register, does that mean I have to send the serial data 8 times faster? (or divide the clock by 8) in other words, How does synchronization happen between the clock and serial inputs of the shift register?

2. I want to connect several shift registers together for a rather large LED display. Whats the technique here?

3. What would be a good method to use to effect the intensity of the display? most likely with PWM...

this is a pdf very similar to the circuit I am building, but I don't have the code for it:

https://www.electro-tech-online.com/custompdfs/2010/09/MLS.pdf

 

[keny]

ok delving into my own murk, I have figured it out to a point using an arduino tutorial:

The 74HC164 Shift Register and your Arduino

But I'd still like some ideas on PWM and perhaps a way to eliminate all the led's from flashing when I load the shift register...

 

[LTX71CM]

You might look at the 74HC595, it has the ability to load all bits and then uses a pin to latch the shift register to the storage register. That solves issue of the LEDs flickering while loading the display. For problem two, PWM, you can use the output enable pin on the 74HC595 get the effect you want.

 

[keny]

I'm thinking about it. Whats the scoop with daisy chaining the 595? same deal? I need 8 x 24! (or more eventually) are there 16 bit or greater versions available?

My current workaround is to stall as long as possible then the issue only appears when the LED's change.

I also turned off the transistor from the MCU so the lights aren't on at all while the shift register is loading. Now they all turn off as the shift register loads, so the lights flicker but at least unwanted lights arent illuminating.

 

[Pommie]

Have you considered something like the Max7219. It can drive an 8*8 array of LEDs.

Mike.

 

[AtomSoft]

The 595 are a great IC to have and use. I learned a ton from here:

Arduino - ShiftOut

Its arduino based but converted to PIC easy. Since it explains a ton!!!