jrSASI INTERFACE BOARD CONSTRUCTION HINTS AND TIPS December 21, 1985 I. Introduction Thoughout this text the terms "board", "interface board" and "jrSASI board" will be used interchangeably to refer to TPL Corporation's design for an IBM PCjr SASI hard disk interface board. What follows will make a great deal more sense if you have first studied JRSASI.TXT which gives the PCjr SASI project details and JRSASI1.SHM through JRSASI4.SHM which contain the interface board schematics. TPL, as the designer of the PCjr to SASI interface, has naturally built quite a few of the boards. In doing so, we developed some useful hints and tips which make the construction that much easier. This document is not a step- by-step "HeathKit" type set of instructions for building the jrSASI board. We are assuming a level of experience in board construction on the part of the reader/builder which renders step-by-step instructions unnecessary. Here instead, we offer those hints mentioned above which have helped us and can help you too. The jrSASI board, as you can gather from the schematics and the parts list, has only 15 chips and just a handful of discrete components (mostly resistors). We estimate it takes about 15 hours to complete the jrSASI board once all parts and tools are available. We usually spent 3-4 nights building each board. Once we were in a hurry and built one in just 2 nights (6 hours per). Under no circumstances should one attempt to build the board in less than a couple of nights. You would be amazed how fast mistakes multiply when you are tired. Besides, anyone can use a break after a solid 2-3 hours of wire-wrapping. It is far better to invest extra time building now rather than waste time later trying to figure out why the board you built in "just one day" doesn't work. II. Preparation After getting all the parts in the parts list from your favorite electronics supply house, the next thing you will need is a large well-lit area to work. As we saw above, the board takes at least three evenings to build. Your chosen work area must be capable of remaining undisturbed by spouses, kids and yourself for such a period. What about tools? Assemble these next. You will need (at the very least): - A pencil - Some paper - A red fine-point felt-tip pen - 2 copies of the schematics - A fine-tipped low power PC-board type soldering iron - Fine rosin-core solder - A wire wrapping tool - A wire-wrap wire stripper - Wire-wrap wire (30 gauge) (If you can get this in pre-cut, pre-stripped lengths, by all means do so!) - A side cutter (also called diagonal cutters) - A small needle nose pliers - An ohm-meter In the following we assume that TPL's PCjr Prototyping Board (of course!) and wire-wrapping are the basis for your board's construction. We might be biased, but if you're not using our proto-board you will have to do a lot of extra work to interface to the PCjr's expansion connector. If you are not wire-wrapping, you may be using insulation displacement sockets or point-to- point soldering. No matter how you choose to build your jrSASI board, please read this document completely since the majority of the hints offered apply to any type of assembly method. With all the parts and tools ready, we can begin by preparing some things to help with the construction. The first is a drawing which shows where each part is to be placed on the board. A suggested placement for the parts is shown in JRSASI.TXT. Copy or print this drawing. This is what the top (component side) of the finished board will look like. This is nice, but most of the work will be done on the bottom (solder side). Get a bottom-view of the board by holding the layout sheet up to a window and tracing the chip outlines on the back. Each chip on the layout sheet has a number (U1-U15) matching that of a chip in the schematics. In each chip rectangle write its number and pin 1 location to complete your "mirror- image" view of the bottom of the board. Now when you are adding wires you can figure out which chip is which at a glance. Besides knowing where the chips are, you will need to know what connections have been made and which are yet to do. This is where the red fine-tipped marker and one of the two copies of the schematics comes in. Take a copy of the schematics and write "wire-up" at the top. As each wire is added you you will trace the line(s) representing the connection with the red pen to mark this connection as done. III. Assembly The first step in building is to mechanically secure the parts to the board. The special 60 pin PCjr I/O connector is the first thing to be installed. The directions supplied with the PCjr Prototyping Board explain how this is done. Mount the 50-pin header next. From the top view layout we see it goes very near the right-hand edge of the board with pin 1 pointing upward. Pins 1 through 49 must be connected together and then to Ground. Completely strip a wire long enough to span these 25 pins plus extra to reach a grounded pin of the PCjr I/O connector. Solder the wire to each pin and each pin to the proto-board. If the header has wire-wrap leads, you can go ahead and solder pins 2-50 for strength. If the header has short leads (such as for use on a printed circuit board), leave the soldering of pins 2-50 until later when you are actually connecting wires to them. Connect the wire from pins 1-49 to Ground and mark the wire-up schematic accordingly. NOTE: You may want to solder wire wrap studs to the PCjr I/O connector pins which are listed as having connections in the schematic. This allows you to wrap rather than solder. One advantage of wrapped connections is that they are easier to undo if found to be incorrect. The network of 220 (red, red, brown) and 330 (orange, orange, brown) ohm resistors can be built next. The resistors are arranged as shown below next to the 50-pin header. _______________________ | 220 330 Pin 1 | TOP SIDE ___ ___ __ | RIGHT-HAND EDGE -(___)-(___)- |::| | -(___)-(___)- |::| | . . . | . . . | ___ ___ | -(___)-(___)- |::| | -(___)-(___)- |__| | Pin 50 | ______________________| Bend the leads and insert each resistor into the board being careful not to confuse any 220's for 330's or vice-versa. Hold the resistors in place with tape and turn the board bottom side up. Coming through from the center of each 220/330 pair is a 220 lead and a 330 lead. For each pair solder these two leads together. With the side cutters clip off one of the two excess leads at each junction. The other leads will have connections made to them later. The unconnected leads of each 220 ohm resister can now be soldered together and then to a +5 volt pin of the PCjr I/O connector. One way to do this is to bend the top and bottom resister leads down to meet each other and meet with the middle resistor leads and then soldering each lead inter- section. Another way is to completely strip a length of wire and solder each resistor lead to it. Either way, clip of the excess lead lengths and solder the connected leads to +5 volts at the PCjr I/O connector. Repeat the procedure for the unconnected 330 ohm resistor leads, but solder them to Ground at the I/O connector after soldering them together. Remove the tape which is no longer needed to hold the resistors and mark the wire-up schematic to show each resistor's connection to +5 or Ground and to each other. Now, refering to the top-view layout, install each chip socket. The board looks neater if the sockets are lined up on the same rows of holes and the board is easier to work with if there are at least 2 rows of holes between sockets and all pin 1's point in the same direction (usually left or up). Secure each socket by soldering two diagonal pins. Solder the capacitor and 10K ohm resistor into place above chip socket U2. Do not clip off the excess lead lengths as they will be used later to make connections to these components. Unplug the soldering iron for a while. The hard part is over or is just beginning depending on your disposition to wire-wrapping. If you are not using pre-stripped wire, it is a good idea to strip a bunch ahead of time and pretend that you are. An easy way to do this is with a wire stripper clamped in a vise. Do one end, snip off a suitable length from the roll with the side cutters and strip the other end. You shouldn't need wires longer than 6 inches and most will be much shorter. Do an assortment of 2 inch and 4 inch lengths to start. It is hard to strip the second end of a wire much shorter than 2 inches. If you read the documentation supplied with the TPL PCjr Prototyping Board then you know that due to the PCjr expansion scheme designed by IBM, that there is not much room between any sidecar (including TPL's proto-board) and the PCjr system unit. This fact adds an extra step when wire-wrapping is used with the proto-board. After all wiring is completed, all but about 1/4th inch of each wire-wrap pin must be clipped off. This is so the proto- board can get close enough to the system unit to contact properly with the PCjr 60 pin I/O expansion connector. We mention this now, before any wires have been wrapped so you can keep this in mind and try to limit the number of connections to any wire-wrap pin to two where possible. Insulation Displacment sockets avoid this problem, but are more expensive and not as readily available. The first things to wrap are the power and Ground connections to each chip. The proper pins for a given size chip are: Number of pins Ground pin +5 pin ===================================== 14 7 14 16 8 16 20 10 20 Pick a chip to start with and wrap a wire from its power pin to the next chip's. Repeat until all power pins are connected and then bring a wire from the last chip's power pin to a source of +5 at the PCjr I/O connector. Do the same for the chip Ground pins, but connect the last one to Ground at the I/O connector. From the schematic you may have noticed other pins of some chips which also need to be brought to +5 or Ground. These connections should be made next. Be sure to mark each with the red pen as you go. The power and Ground buses are done so we can move on to the signal buses. These buses are indicated on the schematic by several wires which take a similar route (all from chip A to chip B, for example). The major signal bus of the jrSASI board is formed by the interconnections between chips U4, U9, U12 and U14. Care should be taken as this bus is wrapped since there are many chips and individual connections involved. Double check each wire as you wrap it and refer to the bottom-view layout frequently. After all this wire-wrapping its time to do a bit more soldering. There are several connections to be made from various chips to pins 2-50 of the 50-pin header. Each even numbered pin of the header which has a signal connected to it must also have the remaining long lead of a 220/330 ohm resister pair connected to it as well. For each such pin, first wrap the connection from the appropriate chip to the corresponding pin of the header. Then bend the next 220/330 resistor pair lead over to contact the same header pin as just wrapped. Finally, solder the resister lead to the wire-wrapped header pin. Its back to straight wire-wrapping again. Simply wrap each connection not yet traced in red on the schematic. When you come to the capacitor and 10K ohm resistor, you can wrap the connections on the leads which were left long when these components were originally installed. Since component leads are not true wire-wrap posts, it is a good idea to solder the wires after they are wrapped. After soldering, the excess lead lengths can be clipped to about 1/4th of an inch long. IV. Checking Your Work With the last connection made, its time to double check your work. First, is the schematic wire-up copy a complete sea of red or is there one sneaky little connection that was missed? When after inspecting the board you feel confident that things are looking good, its time to check each con- nection with an ohm-meter. "Ohming out" the board is perhaps the least fun part of the build process. Oddly enough, it is probably the most important. To you it looks as though the board is done and could be tried out immediately. This is untrue since a board that has mistakes can hardly be considered done. Ohming out the board makes sure that everything that is supposed to be connected is and that things that are not supposed to be connected aren't. The ohm-out step needs a guide as to which connections have been verified just as the wire-up step needed a guide as to which connections have been made. Take the second copy of the schematics and mark it "ohm-out" at the top. As you check each connection, trace it red on this second copy just as you did on the first copy for each wire added. After calibrating the ohm-meter, the most important thing to check is that there is not a direct short between +5 and Ground. Note that even though the chips have not yet been installed, the resistance between a source of +5 and Ground is not infinite because of the 220/330 ohm resistor network. There should be a small amount of resistance between power and Ground (100-300 ohms) but NOT zero resistance. Assuming power and Ground check out, proceed to check each connection and mark it off on the schematic when verified. V. Final Assembly and Applying Power When the ohm-out schematic copy is also a sea of red and you are positive that you have left Murphy and his Law coughing in the dust, the only test left is the acid test - applying power to the board. There are two final-assembly steps to be completed before this can be done however. The first is to clip off all wire-wrap posts to about 1/4th of an inch as mentioned earlier. Next, each integrated circuit should be installed into its proper socket making sure that pin 1's are in the right place. Be careful of excess static charges when handling the chips and make sure that all pins of each chip actually go into their sockets rather than bending too far and folding over flat. The board is ready to be plugged into the PCjr. Power down the Junior and remove that cover plate from the right-hand side of the system unit (or last sidecar expansion unit) to expose the Junior's 60-pin I/O connector. Press the jrSASI board into place on the I/O connector making sure it is seated properly. Being ready to turn off the juice at the slightest hint of trouble (smoke, crackling noises, sparks, etc), turn on the monitor and the PCjr. The IBM logo and the color bars should be displayed and the system memory should count up as it is being tested. In other words the system should behave as though your new jrSASI board is not even installed. It should boot from your favorite system disk without trouble after all the memory is tested. If things seem okay, you are ready to consult JRSASI.TXT for details on connecting the SASI board to a SASI Hard Disk Controller and Hard Disk and actually bringing the disk up (formatting, etc) using the supplied utility software. VI. Troubleshooting You only need to read this section if things didn't seem to work when you applied power or when you tried talking to a hard disk. There any number of reasons why a board which ohms out correctly might interfere with the Junior's operation or won't work when connected to a hard disk. Some of these include: - The board has as yet undetected shorts or wiring errors - One or more chips are bad - One or more ribbon cables are bad - The SASI Hard Disk Controller is bad - The hard disk itself is bad - The hard disk is not properly terminated - A connector, header or cable is installed upside-down or backwards These are merely possiblities to consider and are not in order of likely- hood. Effectively trouble-shooting a board of this type usually requires an oscilloscope and other special equipment. Unfortunately, a description of trouble-shooting techniques would be a small book in itself and will not be undertaken by us at this time. If you used care and followed the schematics and these hints, there is an excellent chance that your board will work the first time you try it. The last section of SDUTIL.DOC offers a more comprehensive guide to trouble-shooting the jrSASI interface. Happy building! Jon Kosmoski V. P. of Software Development Turning Point Logic Corporation