Pin Direction

Yes, the descriptions for pin directions are confusing, particularly for

SUPPLY and POWER.  These words mean pretty much the same thing and the

description doesn't help distinguish the difference very well.

Basically, use SUPPLY only for symbols meant to indicate a supply net in a

schematic, like for a ground symbol.  Use POWER for power and ground pins

of a IC.  The 7805 should have the ground and power pins set to POWER.

The general idea of distinguishing between these pin types is good, but

there are two serious problems with this in Eagle.  First, POWER pins are

automatically connected to a net matching the pin name if such a net

exists.  That is a really bad idea.  I suppose someone thought they were

saving us a little work, but I really really don't like the software making

connections I didn't explicitly define.  To do it without even a warning or

hint takes it from bad to downright irresponsible.

The second problem is when you run the ERC it will complain about POWER

pins connected to nets of different names than the pin name.  This is quite

annoying since these warnings can make it hard to notice a legitimate

problem in the list.  This has also been brought up here for a long time

but Cadsoft has so far refused to budge.  Maybe this will finally be fixed

in version 6.

--

Web access to CadSoft support forums at www.eaglecentral.ca.  Where the CadSoft EAGLE community meets.

On 11/3/2011 2:59 PM, Olin Lathrop wrote:

Yes, the descriptions for pin directions are confusing, particularly for

SUPPLY and POWER.  These words mean pretty much the same thing and the

description doesn't help distinguish the difference very well.

 

Basically, use SUPPLY only for symbols meant to indicate a supply net in a

schematic, like for a ground symbol.  Use POWER for power and ground pins

of a IC.  The 7805 should have the ground and power pins set to POWER.

 

The general idea of distinguishing between these pin types is good, but

there are two serious problems with this in Eagle.  First, POWER pins are

automatically connected to a net matching the pin name if such a net

exists.  That is a really bad idea.  I suppose someone thought they were

saving us a little work, but I really really don't like the software making

connections I didn't explicitly define.  To do it without even a warning or

hint takes it from bad to downright irresponsible.

 

The second problem is when you run the ERC it will complain about POWER

pins connected to nets of different names than the pin name.  This is quite

annoying since these warnings can make it hard to notice a legitimate

problem in the list.  This has also been brought up here for a long time

but Cadsoft has so far refused to budge.  Maybe this will finally be fixed

in version 6.

Thanks for your explanation.  I agree it is a terrible idea to

automatically connect these pins to a net, especially when the "stock"

library components have inconsistencies in how pins are designated.

Am 03.11.2011 19:32, schrieb John Friede:

I am a new Eagle user. The more I read about pin direction (ie. I/O,

PWR, IN, Out, etc) the more confused I get. After reading some

tutorials, it would seem that for a voltagge regulator such as the

78LXX, the ground pin should be to "PWR". In the v-reg.lbr included with

Eagle however, ground is set to "In" and out is set to "Pas". This is

inconsistent with an LM2596 in national-semiconductor.lbr that sets

ground to "pwr" and out as "out".

 

How important are these labels really? Some posts I have read just say

to ignore the ERC warnings generated by inconsistencies. That doesn't

seem like a solution. I am about to layout a somewhat complex board that

will have grounds on one side isolated from grounds on the other. How

will these direction labels affect me?

 

Thanks

The direction is the base for calculation in ERC. If two inputs are

connected together nothing may happen, if two outputs (totem pole)are

connected together you may have a short circuit. On the other hand it is

quite normal to tie a couple of outputs together if these are open

collector. (Help Pin for further info). An input may be left unconnected

by some devices but you would get an error message from eagle. So it may

be better to mark those inputs as passive.

A vcc supply symbol provides power, the pwr pin of a device consumes

power. Usually one puts a +5V symbol onto the outgoing net of a 7805.

If this net was declared as pwr and you attach a aupply symbol to it,

then the 7805 is consuming power (logically) instead of delivering it

An easy way may be to mark every thing as passive but then you will get

no warnings at all. I think it is better to get a warning to check and

acknowledge it before overlooking something.

A litle problem may be microcntrollers, where most of the pins are I/O

and the direction is set later by the program.

If you want to use the help of the ERC you should see that the direction

is correctly set especially if you create your own libraries.

--

Mit freundlichen Grüßen / With best regards

Joern Paschedag

John Friede schrieb:

Thanks for your explanation.  I agree it is a terrible idea to

automatically connect these pins to a net, especially when the "stock"

library components have inconsistencies in how pins are designated.

I think that the libraries have grown over the years, with different

and/or changing authors...

By looking at them, you learn that the only libraries you can really

trust are those you created by yourself.

Tilmann