confusion with the CD74HC165 8 bit register

[lerameur]

Hi,

I am just trying to use the CD74HC165 chip to see the serial 8 bit output, but its giving me nothing. I do not understand the PL, CP and CE ports, and there no explanation in the datasheet, can some explain to me these three ports??

thanks

K

[HenrikOlsson]

Hi,
The '165 is an 8bit parallel in/serial out shift register. If reading it with PBP you use the Shiftin command. I mention this because you say you're trying see the 8bit serial output which to me sounds as if your trying to use with Shiftout. The DS input of the chip is a serial input but there's no way to "see" the data being shifted in, it's used to shift data "thru" the device when cascading several '165's.

OK, the PL input is what "loads" the 8 bits of data (D0-D7) into the internal shift register. CP and CE are the two clock inputs, CP is active high, CE is active low.

This datasheet has a pretty good description of how it works.

/Henrik.

[lerameur]

I was trying to use serin command. Cause the chip is parallel in - serial out. Do I need to sent a special signal for CP, or PBP takes care of that ?

[HenrikOlsson]

Serin is for asynchronous serial communication and can't be used with that shiftregister. You need to use Shiftin which is for synchronous serial communication.

With the Shiftin command you specify two pins, one for the data and one for the clock. First you need to load/latch the data into the shiftregister by pulsing the PL pin, then the Shiftin command is used to shift data out of the '165 and into the PIC.

[lerameur]

I understang you are mentionning two pins, one clocking and one input. Although the datasheet mentions PL and CP for input, Then Q7 for serial output. That would mean three pins, so we dont need CE pin ??.

K

[lerameur]

I think I have things cleared up. Data is Q7, Clock=CP, Pulse=PL (send a signal to receive the byte with shiftin command) and CE is grounded. ?!?