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CY74FCT244T: CY74FCT244T Maximum Input Signal Frequency

user5766736
Prodigy 50 points
Part Number: CY74FCT244T
Other Parts Discussed in Thread: TS5MP645, TS3A5018

Hello,

I consider to use CY74FCT244T for JTAG bus switcher. At this point I saw tplh and tphl timing values but is there any input signal frequency limit for input signals? Also can I use this IC for bidirectional discrete signal buffer? As I understood from the datasheet, chip works as unidirectional signal buffer. 

Regards,

Dogancan 

  • 0
    Guru 243220 points

    '244 buffers are unidirectional.

    What do you need the buffer for? Disconnecting from the bus? Increasing drive strength? And what frequency do you need?

  • 0 in reply to Clemens Ladisch
    Prodigy 50 points

    Hello,

    Actually, I want to connect main JTAG bus of FPGA to two different connectors and also want to enable only one connection to the connectors (like a multiplexer). By doing this, I want to prevent stubs on the JTAG line. 60 MHz is enough for me. Also I want to connect 3 bidirectional discrete signals, which are very low speed,  to these connectors and again want to enable one connector connections. In addition, I have to switch buffers depends on the my application scenario. Sometimes, first buffer and first connector connections will be enabled, sometimes the other connection and the other buffer. I hope everything is clear about my application now.

    Regards,

    Dogancan

  • 0 in reply to user5766736
    TI__Mastermind 42600 points

    Hi Dogancan,

    This device is unidirectional so it won't be  able to handle bidirectional signals. My recommendation is to use a transceiver of some sort which will allow you to control direction. So there are 7 signals going to two connectors in which you want to be able select which connector is being used? What supplies do you have to work with?

  • 0 in reply to user5766736
    Guru 243220 points

    As far as I can see, you do not need buffering, just a multiplexer. (And in any case, bidirectional signals cannot be buffered without a separate direction signal.)

    Assuming 3.3 V, the smallest mux with at least 7 channels actually has 10 (TS5MP645). If cost is more important than space, use 2x TS3A5018.

  • 0 in reply to Dylan Hubbard
    Prodigy 50 points

    Hi Dylan,

    I need to use 3.3V supplies in my design because our JTAG bus is working with 3.3V. At the below discussion, I think Clemens' solutions (exactly the TS3A5018) is compatible for my design. As I understood from your post, you offered the same technique as a solution. Thank you for your interests and time. 

    Regards,

    Dogancan    

  • 0 in reply to Clemens Ladisch
    Prodigy 50 points

    Hi Clemens,

    I think 2x TS3A5018 solution is very compatible for my design. Thank you for your interests and time. 

    Regards,

    Dogancan