Alright! You've read up on the sites that talk about wirewrapping, you've ordered your parts, and you're ready for the next step. The first thing you'll want to do is look over the schematic, or wiring layout, of the board. I've drawn it as a high-res GIF, suitable for full-page printing on a standard 8.5x11 page. Be sure to print it in landscape, and use your printer's finest black-and-white quality setting. Your eyes will thank you for it.
Download it here. I'd recommend saving
it to your local machine.
Here is the same schematic in an easier to read Adobe Acrobat version.
Experienced builders will note that there's no provision for buffering, or other PC protection. This may be dealt with in the future, but for now, just be slow and careful in your wiring and you'll be OK. I'm running the exact same configuration here, with no problems.
Before you go further, you might want to read my info on the PC bus, the 3-8 decoder, the 7266 encoder chip, or a bit about encoders and how they work.
First thing on the to-do list is attaching some kind of bracket to the end of the card, so that you'll have a way to firmly mount the card into your PC. Look inside your PC, and examine the metal plate that faces the back of the computer. In my case, the fastest fix was to steal the bracket off a similar card, and drill the prototype board to suit. Old sound cards, modems, or the like are a good source for raw materials. Be sure to complete this step first, since doing it after the wirewrap is a big mistake. 9 times out of ten, you'll weaken or break one of the connections, and you'll go nuts trying to find the error.
Get out the DB-25 connector you got from M.P. Jones, and stick it in the spot that's made for it, right at the end of the board. You'll probably need to cut a hole in the bracket so that the cable can be connected (Hey, metalworking content! We can do that! :). Look really close at the back of the board and you'll see traces going from the pads under the connector and off into the protoboard. We'll use a soldering iron to solder the connector down, and then use the wirewrap posts in the appropriate hole on the board to make our encoder connections. You'll only need to put solder on about 10 of them. That will give it the electrical contact for the encoder signals, and enough solidity to stay on the board. You can hit all the pads with solder if you really want to make it strong, but be sure not to join pads with a bridge of solder.
With that done, we can prepare the board for wrapping. Get out the T44 miniwrap terminals you got from Digikey. They're the little things that look like spikes. Insert them through the board, from the front to the back. To make sure you insert them right, orient your board to look like the picture below. That's the front side. Then just drop the pins in. Read on to figure out where you should drop them.
OK, the first order of business is to determine what row A is, at the base of the card. Look really close to the card edge connector at the bottom:
See where it says 'A31' at the left, and 'A1' at the right? Those refer to the lines from the PC bus. If you flip the card over and look in the same place on the back, you'll see 'B1' and 'B31'. What you're looking for is the traces going from the gold edge connector to the thru-holes on the card. On the front, the 'A' lines go straight up to the bottom row, so this is where you'll put the wirewrap posts for row 'A'. On the back...
...you can see how the 'B' traces run around the 'A' row and up to the next. Obviously, we put the 'B' posts in here. Please be aware, your prototype board might be different from mine. I've seen it with row 'A' on top and on the bottom. Make sure you know how your card is arranged.
Flipping the board again, so the front faces up, we can start putting the posts in. Looking at the schematic, we generate a list of where we'll need to add them:
Add posts in A2-A9, A11, A21-31, B1, B3, B13, B14, and B29-31. That's 27 posts. Count them after they're installed, just to make sure.
Right now, you're looking at all these posts wobbling around in their holes, wondering how they are supposed to be any use at all. Well, if we were in a shop with all possible tools, we'd use the proper insertion tool and they'd be seated down tight. We're not, so we wing it. I used a pair of needlenose pliers, gently tugging/wiggling the posts down until they seated. The thing you want to be cautious of is bending or excessively burring the posts. Practice using posts off in the top back section of the board, far from where our work is. Bent posts will cause the wirewrap tool to bind up on the posts stopping you from wrapping wire at the base, where it'll be safer from damage. Get them all seated, and make sure they aren't even close to touching at the top. If a post is questionable, toss it and try again.
Once you have the posts in place, we can place the sockets and start wiring. It's not incredibly important how or where you place them, but you do want to minimize crossing power and data lines, or having the chip-to-bus wiring near the chip-to-outside-world wiring. To avoid confusion, arrange the chips on the front of the board so that they closely match the way I've laid them out in the schematic. Each chip has a little 'dent' in the end or a silkscreened mark that labels pin 1. This dent should point away from the edge of the board that has the metal bracket. To be absolutly sure, place the board front-side up, with the card edge connector pointing at you. The chip dent should be on the left side. Lay the sockets out so the lowest 74LS138 is 5-6 rows above the card edge connector. The LS7166 should also be 5-6 rows from the right of the card, to leave room for whatever external connector stuff we decide to add. To lock the sockets down, I guess you could try gluing them, but I'm not sure. It's one of the things I've missed in self-teaching this stuff. If there's a better way to keep them down, I'm all ears.
OK, time to get to wiring things up. If you've read up on the wirewrap stuff, this will be easy. If you haven't, go do that right now! And be sure to practice if you feel unsure about what you've read. A decent wirewrap tool has 400,000 wraps in its lifespan, and a little practice isn't going to cost more than 50 cents in wire and posts. Don't re-use the posts afterwards. The corners get rounded and reduce the connection quality.
When wiring, take your time. It's usually easier to triple-check the route before you wrap it than to re-wire later. Get it right the first time and you'll save untold hours and more than a few gray hairs debugging. To help stay organized, try wiring the address lines first, then the data lines, then power, etc. The number one thing that will trip you up is that the schematic is as viewed from the top of the board, and you'll be working on the bottom. Take your time and keep this in mind and you'll be fine. Keep your wires as short as possible, and never use a piece of wire that's been bent severly or might have been nicked. Wire's cheap, and again you'll want to minimize the debugging headaches. Even playing it carefully, it should only take 1-2 hours tops.
Head on over to the wiring instructions page and get to it!