74hc589 PISO IC with ATMEGA8

[djc]

HI,

Can anybody plz tell me about the operation of 74hc589 PISO IC. Its PIN 10 i.e Output Enable pin is connected to line decoder so that output is enabled. PIN 9(OH) of it is connected to ATMEGA8 PIN 14. PIN 11(SCK) to MC PIN 17. PIN 12(RCK) to MC PIN 18. PIN 13(SLOAD) to MC PIN 19. PIN 14 has no connection.Switched are connected on PIN 1,2,3 and 15. How it is operated. Plz guide.

 

[djc]

Hi,
I have operated 74HC589 now. First i made latch clock high to low, then load clock low to high. After that i shifted the clock 8 times and stored status of output pin each time in 8 separate variables. But each time i am getting '0' output. Switches are connected on first 4 inputs. Switches are initially pull up so when switch is pressed it gives '0' output else output is 1 or nearly 5v. And according to output i will drive LED connected to 74HC595. What is happening now is even if key is not pressed connected to 74hc589, status of variables in which switch status is stored is giving '0' all the time. So my question is what is the output of 74HC589. In datasheet it is given as 3 state output. What does it mean?

 

[jayanth.devarayanadurga]

SH_CP shifts data into the shift rehister and after shifting 8 bits of data you need to clock ST_CP once to make the data in shift register to load into storage register. Only the data in the storage register appears at the output.

 

[djc]

Thanx jayanth,

However i am facing problem with the 74hc589. It is mentioned in datasheet that it gives 3 state output. What does that mean?Right now i am checking for a single digit, is it correct way to check the output?

 

[jayanth.devarayanadurga]

Sorry, I read it as HC595.

https://en.wikipedia.org/wiki/Three-state_logic

High Impedance state is also known as Z state.

 

[djc]

Thanx jayanth,

But how that logic is applied to 74hc589? in which form it gives the output?