On 5/30/07, Gerhard Fiedler <lists@connectionbrazil.com> wrote:
> Vasile Surducan wrote:
>
> >>> Hi all.  If I use a 74LS245 bidirectional bus transceiver is the
> >>> write-not signal the one to the direction control pin?  Or can either
> >>> the write-not or read-not be used to control the direction?
>
> >> I'm not sure what you mean by "write-not" and "read-not".
> >>
> >> The 74LS245 has got two pins that control the flow, the DIR (pin 1) and
> >> G' (pin 19). The DIR selects if the bus A should move to B, or B to A.
> >> The G' effectively turns the whole bus ON or OFF.
>
> > Depends. If you take a look here: http://www.geocities.com/vsurducan/electro/8255/8255.htm
> > you'll see it's read-not. As I remember read-not and write-not signals
> > are in opposite phase but that depends hardly on your system timings.
>
> I checked three data sheets (Motorola, Texas, ON) and even though they use
> a slightly different nomenclature, all three have an inverted output enable
> (low=on) and a direction pin.
>
> None of them uses the terms "read" or "write". This makes sense, because
> which direction is read and which is write (or if this is about read and
> write at all) is up to the application and is not defined by the chip.
> (They use "A to B" and "B to A" as direction definition.)

This reminds me a topic a while ago about "asserted" and "deasserted".
Sure you have right about the application, but I had the feeling Rich
is inside the board, debugging a data bus...so the answer was for the
question itself.
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