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SN75161B: SN75161 datasheet, port explanation

Robert Wood
Intellectual 420 points
Part Number: SN75161B



Folks,

The above is a snipped form the SN75161 datasheet. (BTW I know this is going obsolete.)

The picture shows the tpyical ports for both kinds of lines. I don't understand it; these are bidirectional ports so they must have an input and an output, but these figures simply say "input/output port". So what is that, the part that's at the outside world? The part that connects to the micro  (the local bus)? Either way up, where is the OTHER end of the connection? So if it's configured as an input, where is the ouput and vice-verse?

Also, the input and output labels look the wrong way round. If you look at the SRQ/NDAC & NRFD port, these need to be open collector, but the open collector is on the left hand side of the diagram, which is labelled input. However, to further confuse things, it says the circuit inside the dashed lines is the output. So which is it? Should the "Input/Output Port" label say "Output/Input Port"? And, as I say, is that in respect to the GPIB bus or to the local logic?

Also, it talks about "driver output" and "receiver output" what is driver and what is receiver? Is driver sending the logic signals to outside world (ie the GPIB bus)? Or is this dependent on the direction set by the DC pin? Is that resistor changed dependent on the state of that pin?

I'm clearly missing something fundamental here and completely failing to follow this datasheet!

Thanks.

  • 0
    TI__Mastermind 46987 points

    Hi Robert,

    We really don't have like any information on these devices beyond what is in the datasheet (they are old and a standard that essentially is non-existent in most modern systems so our information on these parts is lacking) . I agree with you the "eq circuits" don't make a lot of sense because it isn't showing enough detail to show how the connections actually work are where the wires are going (there are 4 or 5 lines that leave the "circuit" block from the circuit schematic but they only highlight one portion). 

    That being said we typically don't include deep dives into eq. circuits (beyond block diagrams) on more modern transceivers (not GPIB) because they aren't necessary for understanding how the device operates and because we don't give full circuits they generate more questions than answers. The logic and block diagrams + electrical specification tables are sufficient for design purposes. But I would strongly suggest to reconsider using GPIB at all if its a possibility (I understand you may not have that choice).

    Best,

    Parker Dodson

  • 0 in reply to Parker Dodson
    Intellectual 420 points

    Problem is this is a Nat Semi device really and the people who knew about it were probably lost in the buyout.

    If I had a penny for every time I'd been told not to use GPIB on this product I'd have £5.63 (*).

    GPIB ain't going anywhere, even as an outdated and crazy system it undoubtedly is. End customer wants it, so they're having it. I obviously have no idea how  many units of these you shift, but I'm willing to bet it's  going to leave a lot of people in the lurch you discontinuing them. I hope you license them to another manufacturer.

    * With apologies to Neil.