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SN74CB3Q3257: May I have some question regarding SN74CB3Q3257?

TAlex Wu
Expert 1200 points

Part Number: SN74CB3Q3257

Tool/software:

Dear Sir:

May I have some question regarding SN74CB3Q3257?

SN74CB3Q3257 for JTAG  design application ,

When Host have JTAG (pull high and pull down resistor) after the signal passes through the SN74CB3Q3257 connect to Client side device.The Client side

device need pull high and pull down resistor for JTAG ,too ?

or The path before and after the  SN74CB3Q3257 can be considered the same line.No need pull high and pull down resistor for JTAG on Client side device?

thanks

  • 0
    Expert 1200 points

    May I have some question regarding SN74CB3Q3257?

    (Question 1)

    SN74CB3Q3257 for JTAG  design application ,

    When Host have JTAG (pull high and pull down resistor) after the signal passes through the SN74CB3Q3257 connect to Client side device.The Client side

    device need pull high and pull down resistor for JTAG ,too ?

    or The path before and after the  SN74CB3Q3257 can be considered the same line.No need pull high and pull down resistor for JTAG on Client side device?

    (Question 2)

    SN74CB3Q3257 for JTAG  design application ,

    When Host have JTAG (pull high and pull down resistor) after the signal passes through the (SN74CB3Q3257 in series with SN74CB3Q3257) connect to Client side device.The Client side

    device need pull high and pull down resistor for JTAG ,too ?

    or The path before and after the  (SN74CB3Q3257 in series with SN74CB3Q3257) can be considered the same line.No need pull high and pull down resistor for JTAG on Client side device?

    (Please see the simplified diagram the Image)

  • 0 in reply to TAlex Wu
    TI__Mastermind 24995 points

    Hello Alex,

    You need pull ups and downs on both sides of the device, because the signal path can closed due to the switch toggling off. 
    The TMS, TDI, TDO, nSRST and nTRST lines always need to be in a known voltage. 

    Thanks,

    Nir 

  • 0 in reply to Nir Gilgur
    Expert 1200 points

    Dear Sir:

    thanks for your reply.

    May I double confirming regarding your reply mention that"You need pull ups and downs on both sides of the device"meaning "each SN74CB3Q3257 input and output both side as attached image condition4 " or meaning "Host side device and client side device both side as attached image condition 2 and condition3 "?

  • +1 in reply to TAlex Wu
    TI__Mastermind 24995 points

    Hello Alex,

    Conditions 1, 2, and 3 are good. Not condition 4. 

    Note, it seems you are cascading the multiplexers. This will negatively affect the signal you are passing through them.

    For more information please see app note.

    Thanks,

    Nir