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SN74HC165: 74HC165 Alternative Chip-Selectn versus Loadn and Tri-state Output

Peter Baxter
Intellectual 430 points

Part Number: SN74HC165
Other Parts Discussed in Thread: SN74HCS16507, SN74AHCT165

I've been using the 74HC165 PISO and 74HC595 SIPO Shift Registers in many designs. 

The 74HC165 PISO has two issues. It uses an active-low LOADn pulse - rather than the preferred falling-edge of a Chip-Selectn line. Also, the output doesn't allow for tri-state high-impedance. Both of these issues require extra parts to make the 74HC165 function like an SPI Bus part.

Is there a preferred part to the 74HC165 that allows for a Chip-select falling-edge type "capture", and a tri-state output?

Thanks

Peter Baxter

  • 0
    TI__Genius 10480 points

    Hi Peter,

    We have many 3-state output shift registers. Take a look to see if any will work for you. You might be interested in SN74AC595 as a tri-state alternative to HC595. You may also be interested in the SN74AHCT165 as a tri-state alternative to HC165, but it requires a 5V input.

    The majority of our shift registers are all active-low LOADn pulse. You can find some exceptions if you search our Universal shift registers, but most are older devices and not very similar to the HC family. For example, the SN74F299 has the all of features you describe, but in general it's not a good replacement for HC family devices.

    Regards,

    Nikki

  • +1
    Intellectual 430 points

    Hi Nikki,

    The question is a tough one. I've searched hard looking for anything - but nothing comes close.

    I recently saw the SN74HCS16507 8-Bit Parallel-Load Shift Registers with Open-Drain Outputs. While it could "sort-of" do tri-states, it still has the active-low LOADn - rather than a falling edge chip-select.

    Incidently, you may want to refer the "SN74AHCT165 8-Bit Parallel-Load Shift Register with TTL-Compatible Inputs" data sheet back to the TI documentation department. On the front page (top right section), it mentions OE, SER and SRCLRn. The block diagram shown, doesn't include any of those signals.

    I'll stay with the 74HC165 and add the extra parts.

    regards,

    Peter Baxter