Pin Direction

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

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