26 Jul
2013
26 Jul
'13
3:21 p.m.
> Secondly, IC pin numbers. Every IC has all the
connecitons
> unambiguously
> described. If the pins all have unique names (like a RAM, or a
> counter or
> a '154 decodoe) then I simply use those names or something obviously
> equivalent to them That is why tyou see things like signal BRA(2)
> going
> to a pin on an 11/03 RAM labeleld A0. BRA(2) is 'Buffered RAM Address'
> bit 2. The 'bit 2' meanming it comes from address line 2 of the
> processor
> eventially. A0 is the pin on the RAM that Intel called A0 in the
> databook.
>
> Nwo, for simpler TTL ICs, I have a convention. For things like AOI
> gates
> I put the pins in alphabetical order from the TTL databook going
> dwon the
> page. And for simple gates I draw them so that the 'upper' pin on the
> schemtic is towards the pin 1 end of the IC. So that, for example
>
>
> ---------|\
> | >o---------
> ---------|/
> U5c
> '00
>
>
> Means
>
> 10
> ---------|\ 8
> | >o---------
> ---------|/
> 9 U5c
> '00
>
> THis may not be obviouus, but all you had to do was ask me...
If forgot to add that the only non-obvious oen is section 'a' of a triple
3-input gat like the '10 or '27. The convention then is
1----|\
2----| >0--- 12
13---|/
While one may want to communicate with an author about
more subtle
aspects of their work, this is such a basic thing I see no need for
asking, and waiting, for an answer about it. I can't say it would
even occur to me to ask, as if you have a convention about it, it
I have sene this convention used so many times that it never occured to
me to describe it.
In any case... The ouptus of all ICs are unambiguous. I don't think there
are any ICs in the HP9830 that have 2 identical output pins you could
confuse. In which case you could simply trace the few signal (often just
2) at the input of the gate back ot the outputs that drive them and 'buzz
them out' with an ohmmeter. It would take less time to do that for the IC
you are interested in than to post this message.
could simply be noted at the beginning or end of the
work, along with
such things as source material identification, dates, table of
contents, etc.
As a matter of preference, when working on something, I don't want to
have to go from the schematic, then to a pinout to interpret what pin
is being ref'd, and then to the device.
And I have the opposite preference I am afraid. I find pin numbers on
scheamtisc to be irritating. In most cases I know the common TTL pinouts
anyway. For anything else I don't mind having the data book open.
Here are some disadvantages to hand-drawing, aside from basic clarity:
1. The low density means the schematic is spread across more pages.
There is no inherrent reason why a hand drawn scheamtic has a lower
component density than a CAD one.
The limitation on the number of compoentns o na bit of ppaer is
obviosuly due to the size of that paper. The limitation for a CAD system
is the size of the 'virtual paper'.
And I find 'large' CAD diagrams to be a right pain. If you want a printed
copy, you either end up with a much reduced copy which is close to
unreadable, or a number of sheets that have to be lined up and stuck
together. I much preer diagrams desigend to be printed or drawn on A4 sheets.
2. The difficulty of modifying and manipulating a
hand-drawing,
along with the low density,
results in more symbolic connections. Symbolic connections,
while of course useful,
are disadvantageous in that it is not readily clear where all
the uses of a signal are.
I think like you imply here I actually prefer symbolic names provided
they are meaningful (I ahve seen commerical multi-page diagrams where the
signals are just A...Z, AA,AB...AZ, etc) There are a few i nthe HP9830
diagrams where I will admit not to pickign the most suitable name.
'KeyDn/' is the obvious one, it's actualyl a general interrupt input to
the CPU. It goet that name becuase the first machien I looekd at was the
hP9810, and the only thing it's used for there is the keyboard.
Yes, a CAD system would have made it easy to change this. But the other
disadvantages mean I did not use one.
3. (2) is compounded in that the drawings are
unsearchable.
With a computer-based drawing, if one wants to find every
reference
to some signal/symbol, one just walks through it with a search.
As an aside, I have never seen a commerical service manaul (on CD-ROM or
whatever) where yuo can search for signal neames on the schematics.
4. I don't expect OCR to be a remedy to (3).
You have your preferences and conventions, I have mine, some may
prefer yours, some may prefer mine.
I think that;'s right. I took a look at your AL1000 schematics (BTW there
are a couple of broekn links there). In the form you have presented them
they are very useful for understnading how the machine works, I think,
but not so useful for actually repairing one. Wpoorkign out what is on
each board, what components comprise each gate and flip-flop (and yes, I
ahve read your conventions, etc) is too much to have to deal with if I
had the machine in bits in front of me.
This wasn't really about your schematic, it was
whether it is
acceptable for anyone else to RE something Tony already has.
Yo uare reading far too much into this.
I will just point out that _you_ raised the issue of my schematics. I
did not mention them at first.
-tony