[SI-LIST] [Re: [SI-LIST]: Wired-AND VS Wired-OR logic]
- From: "Abhijit Mahajan" <amahajan@xxxxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Wed, 24 Apr 2002 09:13:44 -0700
Here is my thinking:
If the connected gates are active low, then the low voltage on the line
is
interpreted as a logic
one. Thus L(low voltage)=1 and H(High voltage)=0.
Which makes sense since a NMOS device will turn on a low voltage at its
gate.
With this in mind, for two open drain drivers, as long as one of the
drivers is ON
then voltage on the
line will be low i.e., the logic driven will be 1. Thus
Driver A Driver B Line Voltage Logic
OFF(0) OFF(0) H 0
* ON(1) L 1
ON(1) * L 1
Which to me looks like the truth table of an OR gate. Read as:
"Either A or B is on, the output is Logic High".
Abhijit.
Anand.Kuriakose@xxxxxxxxxx wrote:
> Hi all,
>
> We can introduce wired-AND logic by connecting 2 or more open-drain (also
> open-collector) outputs together with a single pull-up resister. The logic of
> AND logic results as follows: If one or more of the drivers asserts the output
> to low state (electrically low ), the equivalent output is low, which is how
> an
> AND gate functions. Also the connected signals have to be active-low signals.
>
> I have seen many documents refering to the above scenario as wired-OR logic.
> It
> doesnt make sense. Also the PCI spec 2.2, sec2.1 refers to O/D signals (ex
> INTX#
> and SERR#) as to be capable of introducing wired-OR logic.
>
> So what is wired-OR logic? How do we realise this logic? Does the active level
> of the connected signals make the difference?
>
> Also one more question. When it comes to wired-AND logic, only one device can
> assert its output low. We cannot have more than one device asserting its
> output
> low simultaneously. Am i right in saying so. If yes, is this allowed in
> wired-OR
> logic.
>
> Thanx in advance for all the valuable inputs.
>
> Regards,
> Anand Kuriakose.
>
> ------------------------------------------------------------------
> To unsubscribe from si-list:
> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>
> or to administer your membership from a web page, go to:
> //www.freelists.org/webpage/si-list
>
> For help:
> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>
> List archives are viewable at:
> //www.freelists.org/archives/si-list
> or at our remote archives:
> http://groups.yahoo.com/group/si-list/messages
> Old (prior to June 6, 2001) list archives are viewable at:
> http://www.qsl.net/wb6tpu
>
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List archives are viewable at:
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List archives are viewable at:
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
- » [SI-LIST] [Re: [SI-LIST]: Wired-AND VS Wired-OR logic]
