I actually like to go with option three, which is, find out what the
Atmel / AVR / PIC / Embedded Processor / etc. is actually doing, that is
how it is actually being used in the circuit, with inputs drawn as
inputs, outputs drawn as outputs, busses drawn as busses, control lines
drawn as control lines, so that the component itself somewhat explains
itself, and so that the flow in and out of the part lends itself to good
circuit flow and specifically to easy functional recognition.
As in make the whole schematic understandable, or at least more
understandable.
Yes this means that you may need to draw a different atmel symbol for
different projects or boards, but I think you'll find that if you
break it up right and do a good job that it will be pretty much the same
for most of your designs, or at least most of your designs from one
engineer or programmer (this is because they tend to repeat themselves
and use as much of the old design as possible each time they go off on a
new project (as in the it worked last time and the nothing ventured,
nothing to fail syndromes)).
Anyway, flow? Oh yeah flow. That was something they stopped teaching and
talking about around 20 years ago when everyone decided to go with the
new hierarchical schematics where it all went on 27 sheets of A size
paper which nobody could understand anyway, so the attitude became why
spend extra time worrying about making the individual circuits or
functional blocks easily recognizable or understandable since the whole
thing is garbage anyway.
As a side note, while it may require that the part be a little larger
due to the extra text, If you simply go with the sequential 40 pin
rectangle type of symbol, I would use the full functional description
of the pin, or what I call the dual description or name. For example,
with a 40 Pin Atmel AT90S8515, just as shown in the data sheet, Pin 10
would be (RXD)PD0 and Pin 11 would be (TXD)PD1, because while the pins
are in fact bits 0 and 1 of Port D, they also are dedicated to be used
as the RXD and TXD lines for serial communications. Doing this on the
schematic symbol will go along way in not only making the schematic much
more understandable, but also enable you (or the engineer or programmer)
to have a better chance to spot any errors due to miswiring, prior to
casting the design in FR4.
JaMi Smith
* * *
-Original Message-
From: Matthew Leigh [mailto:[EMAIL PROTECTED]]
Sent: Thursday, April 11, 2002 7:59 PM
To: Protel EDA Forum
Subject: [PEDA] Duplicate pins in schlib
I'm drawing up a library component for an Atmel microcontroller, which
has
a large number of multi-function pins (for instance, pins 32-39 are
either
an 8-bit I/O port or half of the memory bus). I can see two ways of
representing this in the schematic library:
1) Place 40 pins and give each one a title like PA0 (AD0).
2) Place one pin for each function but with duplicate pin numbers (so
there's two of each pin, with different names).
Which, or both, of these methods is legal (Protel 99SE) and which is
advisable?
Thanks
Matthew Leigh
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