Rich asked the question, Vasile answered it.

----- Original Message ----- 
From: "Gerhard Fiedler" <lists@connectionbrazil.com>
To: <piclist@mit.edu>
Sent: Wednesday, May 30, 2007 9:44 AM
Subject: Re: [EE] Bidirectional bus driver direction control


> 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.)
>
> Gerhard
>
> -- 
> http://www.piclist.com PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist 

-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist