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SN54LS673: Cascading Serial to Parallel Conversion Shift Registers

Viraj Patel
Prodigy 130 points
Part Number: SN54LS673
Other Parts Discussed in Thread: SN74HCS595, SN74HC595, SN74LV595A, SN74AHC595, SN54HC164, CD54HC4094, SN54HC595, CD54HC164

Hi, I am looking to use two (2) SN54LS673 shift registers to process 32 bits of information for my application. The SN54LS673 seems the ideal candidate to perform Serial to Parallel conversion.  Shown below in Figure 1 is the basic idea I have for my application. How should I implement two cascading shift registers to count from LSB to MSB? Also, the datasheet does not provide much information about the control inputs and only provides a truth table. Can you please explain how inputs _CS (Pin 2), SHCLK (Pin 3), R_W (Pin 4), _STRCLR (Pin 5), and MODE_STRCLK (Pin 6) work? Can these inputs be shared by Micro GPIO? Please let me know as soon as possible. Thank you.

Figure 1: Serial to Parallel Conversion

  • 0
    Guru 276380 points

    Why have you chosen this particular device? Do you really need a bipolar, military-grade device?

    As far as I can see, the '673 is not really designed for cascading. You can share all inputs, except for /CS, to address them separately.

    If you have selected it because it has 16 bits, then that is probably the wrong choice. You have to cascade anyway, so use four 8-bit shift registers (e.g., SN74HCS595, SN74HC595, SN74AHC595, SN74LV595A).

  • 0 in reply to Clemens Ladisch
    Prodigy 130 points

    I chosen this device because I needed a military grade device in my application. I understand I can four (4) 8-bit shift registers but I want to reduce the number of cascading registers required. You don't recommend SN54LS673 for cascading? 

  • 0 in reply to Viraj Patel
    Guru 276380 points

    LS is a bipolar family, i.e., it uses lots of power, and the output TTL levels do not go up to 5 V. And the '673 is not easy to cascade because SER/Q15 is a shared input/output; you need quite a lot GPIOs.

    The SN54HC595 or CD54HC4094 can be cascaded easily. (When controlling LEDs, you can also use the SN54HC164/CD54HC164.)

  • +1 in reply to Clemens Ladisch
    TI__Expert 7701 points

    Hi Viraj,

    I agree with Clemens here that unless you're really strapped for board space using a bipolar device is typically not advised.

    This app note goes into details about cascading shift registers Designing with Shift Registers.

    This link is all of our military grade standard CMOS serial in parallel out shift registers I would recommend choosing from this list although Clemens has already recommended our best ones.

    Regards,

    Owen

  • 0 in reply to Owen Westfall
    Prodigy 130 points

    Thank you for the information. Yes I am restricted on board space. I will proceed with four 8-bit shift registers since they are surface mount.