1)
Style Shape of the port, which side of the port has a wedge
I/O Type Whether the signals come onto the board or go off the board
for the ERC
Alignment Where the text is in the Port
2) input is input to the sheet.
The sheet is the destination and another sheet has the driving source.
The direction is for the ERC to catch our mistakes only. It has
nothing to do with connectivity.
3) Whichever end you connect a wire to is the hot spot. Or to be more
accurate whatever net has the same name as the port is the hot spot.
Basically all the port does is say that the net on that page with the same
name as the port goes off the page. No graphical connection required.
4) With Ports global no wiring is necessary since all ports of the same
name are connected.
With sheet symbol port connections the sheet entries on the sheet
symbols need to be connected and the buses between sheet entries need to be
labeled. I have had the netlister not connect ports where the sheet
entries had a bus wire between them but no bus label.
5) It is smarter to use ports since they are more controllable. You can
ERC them as to direction and they are more easily understood. Also I don't
think Power Objects will do buses.
Ports and Buses are only connected to the nets by the net names, and any
graphical connection is just for the viewer. This is why it will complain
if you have an unnamed net connected to a port, and why a bus between two
sheet entries needs to be named.
Personally I have used all global, ports global and sheet symbol port
connections depending on the design. Some designs are easier with all of
the port names global, where some work best with just the ports global.
Complex designs with many identical sections work best with sheet symbol
port connections since you can start with the same sheet for each section
and not have it tie all the nets together. I like being able to do the
schematic to fit the design, instead of the other way around. On the other
hand most of my designs are Ports global nets local.
Hope this helps.
Rob
[EMAIL PROTECTED] on 06/11/2001 09:52:18 AM
Please respond to "Protel EDA Forum" <[EMAIL PROTECTED]>
To: "Protel EDA Forum" <[EMAIL PROTECTED]>
cc: (bcc: Rob LaMoreaux/DSPT)
Subject: [PEDA] Explanation of Ports
We are trynig to clean up our design process by, among other things, going
to
a convention where net names are local to a sheet and module ports are
global. But I'm having trouble understanding how the attributes of a port
interact, and how they are meant to be used to ensure a well-documented,
ERC-able design.
1) Can someone explain what these port attributes do?
Style
I/O Type
Alignment
2) In this context, does "input" mean that the port acts as an input; i.e.,
I
should be driving it with a signal on this sheet, with the destination on
another sheet? Or does it mean that the signal is an input to this sheet,
connected to one or more input pins on the sheet, and driven by some other
sheet? Your perspective completely reverses the interpretation when you're
looking at a port.
3) What determines which end of the port is the electrical hot spot? Both
ends seem to be active.
4) With a netlist setting of Ports Only Global, is there any requirement to
wire up the sheet entries on the next level up?
5) Is it smarter to just use power objects instead of ports, and avoid all
these issues?
Steve Hendrix
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