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AM26C32C: RS422 trigger signals selection and distribution for AM26C32CD and AM26C31MDREP

TAKANORI ENDO
Prodigy 10 points
Part Number: AM26C32C


We are trying to implement a function to select one from multiple RS422 specification trigger signals (pulse signals of several hundred uss) and a function to distribute the selected one to multiple.

The parts used are (IC-A) 422 receiver: AM26C32CD and (IC-B) 422 driver: AM26C31MDREP.

-Use three of (IC-A) to convert each of the three RS422-spec trigger signals into a single-ended signal.

-Integrate the three outputs (single end) of (IC-A) into one in a pattern, and connect them to the eight inputs of two (IC-B).

-Control the G / G bar signal of ① and select only one trigger signal.

 -The selected trigger signal is output as a 422 signal branched into 8 systems.

I would like to confirm the points of concern when designing the circuit.

Q1.  Is it possible to branch the signal into 8 branches in terms of the output capacity of (IC-A) and the input capacity of (IC-B)?

Q2. Is pull-up or pull-down processing necessary for the output of (IC-A)?

Q3. Is it necessary to provide damping in the wiring between (IC-A) and (IC-B)? If so, what are the wiring and damping resistance placement requirements?

Q4. Are there any other points to be aware of or concerns? Thank you for your cooperation.

  • 0
    Guru 317480 points

    1. CMOS outputs and inputs have a very high fanout. This is no problem.

    2. The driver's A inputs must never float. You need pull-ups or -downs if the receiver's Y outputs are disabled.

    3. You need source termination only if the trace is so long that there are transmission line effects. For a rise/fall time of 4 ns, that would be about 12 cm.

  • 0
    TI__Guru 52542 points

    Hi Takanori,

    Please see below:

    1.  Input current for IC-B is max of +/-1uA with an input at Ground or VCC - the output max current of IC-A is +/-25mA -> branching to 8 inputs of IC-B should be no problem. However if there is any more current draw from the circuit that integrates all three signals it is important to include that in the current budget.  Be aware that the output voltage will drop as output current increases. 

    2. It isn't necessary for IC-A's operation but to ensure a known voltage input on IC-B in cases where IC-A's output is floating a pull-up or pull-down would be necessary - a pull-up is typically used more often than a pull-down. 

    3. Clemens is correct here - the source termination is only necessary for longer wires (about 12cm in this application with this part)

    4. The only possible concern I have is how the signals are being integrated outside of A - I doubt it is much, if any, problem however its the only unknown that I see and because of that I am not sure if there are any risks added.

    Please let me know if you have any other questions!

    Best,

    Parker Dodson