At 08:28 AM 3/7/01 -0600, David Cary wrote:
>I think that that the ``Design | Create Symbol from Sheet'' dialog box asking
>about "Confirm: Reverse Input/Output Directions ?" is pretty silly -- the
>right
>answer is always "No.". Is there ever a good reason to hit "Yes" ?
Hmm... If the right answer is always "No," then is there any good reason to
ask if there is ever a good reason to hit "Yes?"
:-) May I suggest reversing the order: questions first, conclusions
afterwards....
Recently this was discussed here. Using the premise but not the conclusion
of another writer, a port's input/output parameter represents, on a sheet,
the electrical character of devices off of the sheet.
So if there is a device on a sheet with an input, and that input is wired
to a port, presumably that port could be given the attribute "output."
On the next level up, a sheet entry wired to that port would have the
attribute "input," because it represents the input existing on the lower
level. Thus the input/output directions would reverse between the port and
the corresponding sheet entry on the symbol.
Theoretically, then, one would be able to electrically check an individual
sheet without checking the entire hierarchy.
That dialog leads me to suspect that this was in the mind of the designer.
However, the right hand knows not what the left hand is doing; it appears
that an input port connected to an input pin, with nothing above or
horizontally connected to the input port, and with the lower level
schematic checked by itself, does not generate a floating input warning.
Neither does an output port.
There are other complications; if one were following the system I am
describing, some of the ERC matrix settings should be changed from the
default, I think, and there should be checking such that an input port
connected hierarchically (by name) to an input sheet entry on the symbol
for the sheet on which the port lives would be flagged as an error. I don't
know if this is the case, I need to do more research.... It seems to me
that this aspect of ERC is a bit of a mess....
[EMAIL PROTECTED]
Abdulrahman Lomax
P.O. Box 690
El Verano, CA 95433
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