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From: Commander Dave on 18 Oct 2009 18:56

<a7yvm109gf5d1(a)netzero.com> wrote:

> On Oct 18, 1:52 pm, "Commander Dave" <cmdr-d...(a)spamcop.net> wrote:

>> Hmmmm... from what I see of the web sites you provided, my use of "beg a
>> question" is a bit different than you interpreted it. The reason that I
>> even
>> put that in there is that I am a bit gun shy. From all my years on the
>
> There's only one way to "beg a question". But you can beg for our
> attention. But you don't need to.

I defer to your superior knowledge of the subject without agreement or
disagreement. Next time I will write it out fully so everyone including
English majors can understand. It will be longer and more annoying, but at
least it will be correct.

>> newsgroups, I find that there are multitudes of rude people out there
>> ready
>> to criticize even the slightest mistake or question. In some cases it is
>> related to the post and sometimes not. For example, they may nitpick your
>> methods, design, reasoning, schematic program, operating system,
>> terminology, etc. Others like to pick at things like "bottom posting is
>> best" or that you are a loser because you mispelled a word or used poor
>> grammer. All of these type things are non-helpful, especially when
>> pointed
>
> I disagree. Any information is useful eventually. Correct usage of
> expressions and logical fallacies is important.
> You ever met someone who says "for all intensive purposes" for
> example? Or professional websites where the old it's/its problem shows
> up? What else did they get wrong?

May I suggest that there is a good balance point? In a non-professional
setting such as newsgroups, there are times when it is appropriate to
correct and when it is not. For example, if I WROTE IN ALL CAPS, I would
expect to get a spanking. Or I would even accept a correction of "verticle"
to "vertical". But then there are times when it should really just let it
go. It gets very annoying when people correct every little mistake. Have you
ever had a conversation with a person who keeps interrupting you to correct
your useage of "who" or "whom"? Or correct your verb tense? It gets really
annoying fast and you quickly learn to avoid that person in conversation.
When it is done on the newsgroups, it usually causes either a high noise to
signal ratio for the group or long threads that have nothing to do with the
topic at hand. At worst it leads to flame and religious wars (just search on
top/bottom posting for prime examples). I've watched new members leave the
rec.games.video.arcade.collecting newsgroups over the years because on the
first post they made, people nitpicked and acted all condesending. It's
really sad to see.

And as for any information being useful, that is true, but only if it is in
the correct context. There is a time and a place for everything and I find
it a bit arrogant that you would decide an electronics forum is appropriate
for grammer correction, especially since I don't consider it to be a mistake
how I wrote it. You are entitled to your opinion of course, but I consider
your correction to be crossing the line from necessary to just annoyance. If
you don't like my posting style or grammer, it would be best just not to say
anything at all and not be the newgroup policeman. Just put me on the
*plonk* list.

So, to end it once and for all, you win. My grammer is atrocious and I
should be flogged and my posts deleted. I beg your pardon. Now, can we just
drop it and get back to the subject of electronc design?

>> I am glad to see that you agree that I made a good choice. It was the
>> best I
>> could come up with at the time, but this being my first design I was
>> thinking there may be a better alternative. Unfortunatly, the 16C550 has
>> been discontinued in the DIP 40 pin format, so I went with a PLCC which
>> was
>> hard to wire up and probably the reason for my prototype failure. I have
>> an
>> PLCC to DIP adapter on the way that should help with that.
>
> Well, you didn't say if you are planning to make a PCB or keep it as a
> hand-wired proto.

I see I didn't explicitly state that fact, but usually things start out as a
wired prototype and them moves to a PCB stage after the bugs are worked out.
To clarify, I am in the wired prototype stage.

>> I can't argue with that and I appreciate the suggestion. I assume that
>> there
>> isn't much I can do in that regard except keep the wiring as short and
>> simple as possible. Perhaps a ribbon cable or something similar would be
>> the
>> answer. I'm open to suggestions.
>
> You can get better integrity by tossing in more grounds between signal
> wires. Like put a ground between every 4 signals, instead of just one
> ground for the whole ribbon.

Once I get the connector nailed down I'll see how many extra connections I
have and see if I can throw in a some extra grounds in between. It sure
couldn't hurt.

> Also, when carrying power off the main board to a hack, it is wise to
> use a sacrificial resistor as a "fuse", so that accidental shorts
> don't connect the entire power supply of your machine to the short.
> Put the resistor in the machine where your wires start. A couple of
> ohms should be fine.

Would some type of fuse not be indicated? Why is a resistor a better choice?
Is it because that a surge can get through the fuse before it blows but a
resistor won't let it through before it burns up?

>> > Don't forget decoupling caps!
>> > Don't leave logic gate inputs floating, even if the logic family
>> > doesn't mind, it's not good design practice.
>>
>> OK, thanks for the suggestions. I'll have to look up decoupling caps and
>> see
>> if they are needed on the design I have (still shaky on electronics). On
>> the
>
> You don't look it up, you just do it. The "why" can become tricky.
> It's a whole subject in itself.

Yes, but I have no idea what decoupling caps are and HOW they are used.
Before I "just do it", I have to know what they are and how they are used.
I'll try not to get bogged down in theory.

>> suggestion of not leaving logic gates floating, would this apply to all
>> the
>> pins on the 16C550 also? I pulled a lot of information from the net and
>> most
>> of the time I see them just listed at not connected.
>
> It is true that many inputs have built-in pull ups or pull-downs.
> If you leave something floating that shouldn't be, you can get
> anything from overheating components to intermittent operation.
> If you are sure it can be left floating, then it's cool.

I'll double check the design and see if I can spot anything.

>> Thanks for the helpful suggestions!

> Sometimes, this group works.

And sometimes it works, but in an annoying way. But I do appreciate the
help.

-Commander Dave


From: Commander Dave on 18 Oct 2009 18:59

<a7yvm109gf5d1(a)netzero.com> wrote:
> On Oct 18, 4:15 pm, "Commander Dave" <cmdr-d...(a)spamcop.net> wrote:
>
>> I would like to get an oscilloscope, but I am really cash poor. I
>> practically have to scrounge money for the small parts that I buy. One of
>> these days I'll snatch one up cheap, but until I get the money I have to
>> work with what I have.
>>
>> Thanks for the suggestions,
>> -Commander Dave
>
> Where are you located? You sound like someone that can benefit from
> people trying to cleanup their place.

I am in North Alabama near Huntsville.


From: Tim Williams on 19 Oct 2009 01:34
On Oct 18, 1:01 pm, a7yvm109gf...(a)netzero.com wrote:
> Even on an older system with presumably slow clocks and rise times,
> spaghetti wiring like this might cause signal integrity issues that
> will be hard to diagnose if you don't have an oscilloscope.

He's not kidding. I have a simple Z80, memory and output latches on a
breadboard. Wires everywhere, of course:
http://myweb.msoe.edu/williamstm/Images/Z80_Timer.jpg
There's actually more on the board now, since I moved the "ISP" device
onto this board as well. Anyways, as far as signal quality, this
board runs at 4MHz and works fine for the most part. Occasionally I
have had random errors which cause it to freeze. The supply lines are
well bypassed, so I'm guessing a signal line (possibly the clock
itself) is bouncing slightly too far, corrupting the processor's
internal state. Since it's an old NMOS chip, loss of clock = frozen
up hard and needs to be reset.

What's most peculiar is, for a while, I've had it running a cute
chaser on the LED display (scrolling text, flashing lights, that sort
of thing). Recently I changed it so it generates pseudorandom noise
on the display. Ah, but now it freezes up every couple of days.
Sometimes within hours, sometimes a week goes by. Moved around a few
wires, now it hasn't frozen since.

Signal quality is always worth keeping an eye on. If you're adding
wires to your Z80 computer's bus, be mindful that you're changing its
characteristics. More than 12 inches of length will probably lead to
errors, even though those errors may not show up for a long time.
Random numbers are good at *eventually* finding funny errors; programs
running in identical loops forever aren't as good.

Tim
From: Commander Dave on 19 Oct 2009 08:30

"Tim Williams" <tmoranwms(a)gmail.com> wrote in message
news:f26fe857-5560-49ac-b3c1-945c0187467e(a)p35g2000yqh.googlegroups.com...
On Oct 18, 1:01 pm, a7yvm109gf...(a)netzero.com wrote:
> Even on an older system with presumably slow clocks and rise times,
> spaghetti wiring like this might cause signal integrity issues that
> will be hard to diagnose if you don't have an oscilloscope.

He's not kidding. <snip>
Signal quality is always worth keeping an eye on. If you're adding
wires to your Z80 computer's bus, be mindful that you're changing its
characteristics. More than 12 inches of length will probably lead to
errors, even though those errors may not show up for a long time.
<snip>
Tim

While I'm not too swift on electronics, I understand and agree. Currently, I
have the sub-board I am building right on the side of the card cage which is
probably about 3 inches from the connections to the Z80 bus. I'm hoping that
the short distance will be enough to keep away the buglings. Also, this game
runs under 2 Mhz, so hopefully that will contribuite to some stability.

Thanks for the info and help!
-Commander Dave


From: Nico Coesel on 19 Oct 2009 13:01
"Commander Dave" <cmdr-dave(a)spamcop.net> wrote:

>"Nico Coesel" <nico(a)puntnl.niks> wrote in message
>news:4adb732b.902338000(a)news.planet.nl...
>
>> Wiring a PLCC socket is not more difficult than a DIP socket.
>
>Oh, I don't know about that... it was definitely harder for me, but again,
>I'm a newbie at building boards. Another reason I wanted the DIP 40 format
>was so I could breadboard it initially... those PLCC sockets don't fit on a
>breadboard AFAIK. Since I have an adapter on the way (found one for $6.95
>shipped), it's pretty much a moot point now.

Indeed. But through hole PLCC sockets also use a 0.1" grid so they
should fit on you breadboard.

>>You'll need to figure out which pin goes where first though. I suggest you
>> get a simple oscilloscope (a 20MHz will do) to do some measurements
>> (like the port decoding).
>
>I would like to get an oscilloscope, but I am really cash poor. I
>practically have to scrounge money for the small parts that I buy. One of
>these days I'll snatch one up cheap, but until I get the money I have to
>work with what I have.

Or you could buy or a built a logic probe so you can at least see the
level of a signal and whether it is changing.

--
Failure does not prove something is impossible, failure simply
indicates you are not using the right tools...
"If it doesn't fit, use a bigger hammer!"
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