Donn Steward CPUville 8-bit User manual
CPUville 8-bit Processor Register Display Kit Instruction Manual
By Donn Stewart
© 2019 by Donn Stewart
If you find any errors in this manual, please let me know. hanks.
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Table of Contents
Introduction................................................................................................................................................3
Building ips..............................................................................................................................................3
Building the Register Display....................................................................................................................8
esting and Using the Register Display...................................................................................................12
Register Display Schematic.....................................................................................................................13
Register Display Parts Organizer.............................................................................................................14
Register Display Parts List.......................................................................................................................14
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Introduction
Building Tips1
hanks for buying a CPUville kit. Here is what you need to build it:
1. Soldering iron. I strongly recommend a pencil-tip type of iron, from 15 to 30 watts.
2. Solder. Use rosin core solder. Lead-free or lead-containing solders are fine. I have been using
Radio Shack Standard Rosin Core Solder, 60/40, 0.032 in diameter. Use eye protection when
soldering, and be careful, you can get nasty burns even from a 15-watt iron.
3. ools. You will need needle nose pliers to bend leads. You will need wire cutters to cut leads
after soldering, and possibly wire strippers if you want to solder power wires directly to the
board. I find a small pen knife useful in prying chips or connectors from their sockets. A
voltmeter is useful for testing continuity and voltage polarity. A logic probe is useful for
checking voltages on IC pins while the computer is running, to track down signal connection
problems.
4. De-soldering tool. Hopefully you will not need to remove any parts from the board, but if you
do, some kind of desoldering tool is needed. I use a “Soldapullt”, a kind of spring-loaded
syringe that aspirates melted solder quickly. Despite using this, I destroy about half the parts I
try to take off, so it is good to be careful when placing the parts in the first place, so you don't
have to remove them later.
Soldering tips:
1. Before you plug in the iron, clean the tip with something mildly abrasive, like steel wool or a
3M Scotchbrite pad (plain ones, not the ones with soap in them).
2. Let the iron get hot, then tin the tip with lots of solder (let it drip off some). With a fresh coat of
shiny solder the heat transfer is best.
3. Wipe the tinned tip on a wet sponge briefly to get off excess solder. Wipe it from time to time
while soldering, so you don't get a big solder drop on it.
4. All CPUville kits have through-hole parts (no surface-mounted devices). his makes it easy for
even inexperienced hobbyists to be successful.
5. he basic technique of soldering a through-hole lead is as follows:
1. Apply the soldering iron tip so that it heats both the lead and the pad on the circuit board
2. Wait a few seconds (I count to 4), then apply the solder.
3. Apply only the minimum amount of solder to make a small cones around the leads, like this:
1 hese are generic building tips that apply to all CPUville kits. he photos may not be from the same kit you have
purchased.
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his is only about 1/8th inch of the 0.032 inch diameter solder that I use. If you keep
applying the solder, it will drip down the lead to the other side of the board, and you can get
shorts. Plus, it looks bad.
4. Remove the solder first, wait a few seconds, then remove the soldering iron. Pull the iron tip
away at a low angle so as not to make a solder blob.
5. here are some pads with connections to large copper zones (ground planes) like these:
hese require extra heat to make good connections, because the zones wick away the
soldering iron heat. You will usually need to let a 15-watt iron rest on the pin and pad for
more time before applying the solder (count to 10). You also can use a more powerful (30
watt) soldering iron.
6. he three main errors one might make are these:
1. Cold joint. his happens when the iron heats only the pad, leaving the lead cold. he
solder sticks to the pad, but there is no electrical connection with the lead. If this
happens, you can usually just re-heat the joint with the soldering iron in the proper way
(both the lead and the pad), and the electrical connection will be made.
2. Solder blob. his happens if you heat the lead and not the pad, or if you pull the iron up
the lead, dragging solder with it. If this happens, you can probably pick up the blob with
the hot soldering iron tip, and either wipe it off on your sponge and start again, or carry
it down to the joint and make a proper connection.
3. Solder bridge. his happens if you use too much solder, and if flows over to another
pad. his is bad, because it causes a short circuit, and can damage parts.
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If this happens, you have to remove the solder with a desoldering tool, and re-do the joints.
Other tips:
1. Be careful not to damage the traces on the board. hey are very thin copper films, just under
a thin plastic layer of solder mask (the green stuff). If you plop the board down on a hard
surface that has hard debris on it (like ICs, screws etc.) it is easy to cut a trace. Such damage
can be fixed, if you can find it, but try to avoid it in the first place.
2. When soldering multi-pin components, like the ICs or IC sockets, it is important to hold the
parts against the board when soldering so they aren't “up in the air” when the solder
hardens. he connections might work OK, but it looks terrible. If you make a lot of
connections on a part while it is up in the air it is very difficult to get it to sit back down,
because you cannot heat all the connections at the same time. o prevent this, I like to solder
the lowest profile parts first, like resistors, because when the board is upside down they will
be pressed against the top of the board by the surface of the table I am working on. hen, I
solder the taller parts, like the LEDs, sockets, and capacitors. Sometimes, I need to put
something beneath the component to support it while the board is upside down to be
soldered, like a rolled-up piece of paper or the handle of a tool. Another technique is to put a
tiny drop of solder on the tip of the iron, press the part against the board with one hand, and
apply the drop of solder to one of the leads. When the solder hardens, it holds the chip in
place. Solder the other leads, then come back and re-solder the one you used to hold it. It is
good to re-solder it because the original solder drop will not have had any rosin in it. he
rosin in the cold solder helps the electrical connection to be clean.
3. he components with long bendable leads (capacitors, resistors, and LEDs) can be inserted,
and then the leads bent to hold them in place:
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4. You might have to bend the leads on components, ICs or IC sockets to get them to fit into
the holes on the boards. For an IC, place the part on the table and bend the leads all at once,
like this:
Bending the leads one-by-one or all together with the needle nose pliers doesn't work as
well for some reason.
Also, some components have leads bent outward to fit in a certain printed circuit board
footprint, but will fit a smaller footprint if you bend the leads in with a needle-nosed pliers.
Here is a tantalum capacitor, one with wide leads, the other with narrow leads, from bending
the wide leads in:
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5. After you have soldered a row or two check the joints with a magnifying glass. hese kits
have small leads and pads, and it can be hard to see if you got the solder on correctly by
naked eye. You can miss tiny hair-like solder bridges unless you inspect carefully. It is good
to brush off the bottom of the board from time to time with something like a dry paintbrush
or toothbrush, to get off any small solder drops that are sitting there.
6. Some connectors, like headers, have pins that are a little more massive than the IC socket or
component pins. his means that more time, or perhaps more wattage, will be required to
heat these pins with the soldering iron, to ensure good electrical connections.
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Building the Register Display
Print out the Parts Organizer (page 14) and put the parts on the organizer to make sure you have them
all, and to get familiar with them:
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Once you have checked the parts you can start to solder them onto the circuit board.
he easiest way to solder the components is to start with the shortest (parts that lie closest to the board)
and proceed to the tallest. he order is resistors, pushbutton switches, LEDs, IC sockets, capacitors, 4-
position DIP switch, 50-pin connector. he 16-pin receptacle is then soldered to the back.
Some components need to be oriented properly, as described below.
1. he resistors can be soldered first. hey do not have to be oriented.
2. he pushbutton switches are next. he pins have a bend in them that should make them snap
into the holes before you solder them.
3. he LEDs are next. he cathode, which is side with the shorter lead, and the flat side of the
plastic base, is oriented toward the left. here is a small “K” on the circuit board symbol by the
cathode hole:
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Here is a little trick for getting a long row of LEDs to line up nicely, that is, to stand up straight.
he bottom of the LED base is flat, so go down a row, soldering only one lead of each LED
while pressing down on the board. hat way flat bottom of the base will help the LED to stand
upright. hen, before soldering the other lead, bend each LED in the row to get them lined up
well. hen solder the second lead.
4. he IC sockets are next. hey do not need to be oriented.
5. he 50-pin display connector is next. No orientation is necessary, but it has fairly large leads
and may require more time and/or soldering iron wattage to solder.
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Table of contents
