Daisy-chaining shift registers (OE and QH)

Other Hardware General Electronics
1

Quick question about daisy-chaining two 74HC595 ICs.
Does OE (Output Enabled pin) of first IC has to be enabled (LOW) in order for it shift data over it's QH pin to next IC? Wasn't clear to me from Datasheet...

2

If you have two 74HC595, both OE pins are pulled LOW.

3

OE (Output Enable) is exactly what it says.
It enables/disables the OUTPUTS, and has nothing to do with the shift registers.
Normally grounded, but usefull to e.g. PWM LEDs.
Leo..

4

QH' is not affected by OE/ signal.
http://www.ti.com/general/docs/datasheetdiagram.tsp?genericPartNumber=SN74HC595&diagramId=SCLS041I

5

CrossRoads:
QH' is not affected by OE/ signal.
http://www.ti.com/general/docs/datasheetdiagram.tsp?genericPartNumber=SN74HC595&diagramId=SCLS041I

Thank you! Thats exactly what I was looking for! It was really smart of them to design chip like that, I was hoping it for it :slight_smile:

6

bratan:
Thank you! Thats exactly what I was looking for! It was really smart of them to design chip like that, I was hoping it for it :slight_smile:

Well, when they were doing that, the technology was so expensive and cumbersome compared to today, that the basic building blocks had to be designed wisely, to economically cover the most possible uses. I think there was also the expectation that the designs would be around for a long time, which certainly turned out to be true!