SWN being a technically oriented magazine, it is very fitting to review various hardware efforts reported in other magazines, that may or may not have caught your eye. The unfinished series started in Syntax Quarterly Magazine Winter 1982, by John Oliger, 11601 Whidbey Drive, Cumberland, In. 46229, stands out from the crowd as far as hardware projects go. John presented articles describing how to build several different boards; parallel printer interface, expansion board, power supply, 8-16K EPROM board, EPROM programmer and last and absolutely the most, a 64K memory board. This isn’t the end though. Other available works include a 2764 EPROM programmer and a read board, inverse video, power supply, and a memory monitor readout (led). He is presently shipping his TI video upgrade color board which will bypass some of those Sinclair crash and display quirks. [Review next issue.] This is a nice add-on with HI-RES and 40 col screen possiblities.
Instructions given in the three SQ issues are vital to being able to construct most of the boards, so if you don’t have them, get them. Details include how to make your own boards, but considering JLO’s price, you can’t go wrong by buying his. One drawback to these boards is the number of feedthroughs that you must solder in. There are no plated holes (some are now plated through). On the five boards that I built, there were two undrilled holes that had to be fixed. The 64K ram board I received was slightly warped, but this turned out to be a plus. It fits so snuggly in the connector that there is absolutely no wobble! Aside from details on how to make the boards, he gives full schematics and theory of operation as well. For those of you that tried his little modification to enable execution of MC in the 32-48K block and found it didn’t work (SQ D 47 summer 1983), well try again. This time hook up pin 1 and 13 of the 74LS10 to +5V. There apparently was a typo in that issue. (Also, it won’t work with all 64K packs.) Not only is this a hardware project, but it is a software project as well, The printer driver and ASCII conversions must be entered in MC. He Suggests HOT Z for data entry, and gives some how to’s in his documentation, for first timers. I recommend HOT Z as well. HOT Z-II is now available to make full screen editing possible (more on this next time).
The 64K board is really something else. It gives a full 64K, by bank switching the first 8X block with the 8-16K block, decoding either into the 8-16K block. [The actual 0-8K block is unused in most “64K” Rams; in JLO’s it is an alternate 8-16K block. -ed.] If you leave your machine on, it is possible to load those operating system eproms (if the eproms are removable from their boards) into ram, and switch between two different systems occupying the same space! You may also switch out this area in 4K blocks and switch out the 48-64K block. This block is for holding basic programs on 2764 for fast download (I didn’t build this one yet). This board also adds an extra control line, Port Sel not, to decode the printer port (FFFF). In constructing this board, I came up against a seemingly insurmountable number of feedthroughs, but survived none the less. JLO says “90 minutes for this task.” However,I would suggest you plan on making the evening of it. If you goof, it could take a while to trace. The assembly instructions were better for this board than any of the others (thank god). For this reason I suggest tackling this one first. One other great thing about this board is the price. $19.95 bare board, $34.95 kit, not including memory chips. He gives locations for getting the pin 1 refresh 4164 chips. Mine came Federal Express the next day from Microprocessors Unlimited for $53.00. Total cost $88.00 plus a good learning experience (the chip cost is now 1/2 of this price, and you could build this 64K board for about $60.00).
Most of the boards require the expansion board ($10.00) which has the extra port sel not line on it. This board will house 4 boards (the big expansion board is no longer available), This compact board has room for 3-20 pin sockets as well.
You will need at least 6 edge connectors for this series unless you plan on direct solder connections. I found Sintec, in New Jersey, to have the best price at $2.44 each in lots of 10. Remember, you need the extra pin out for port sel not.
The 8-16K eprom read board was the easiest one to construct. JLO suggests two of these. One for 816K and one for 0-6K. This second board is for system mods. You can now start up with a full 64K, repair the LPRINT bug and have your printer use the COPY, LLIST and LPRINT keys. The programmer board was the least explained by the “how to” so be careful building this one. This board has no verify circuitry, which is fine with me. I wouldn’t want to make a living programming eproms with it though. This circuit has it’s own timing circuit which must be fairly precise. It calls for a precision cap and resistor, I used a 500K trimpot and set it with a DVM to 453K. I couldn’t locate a precision 453k resistor anywhere. One other change from the schematics is changing a 180pf cap to 330pf to help with the timing a little.
I don’t have my printer port working yet (still waiting on one chip) so I won’t comment about it at this time. JLO also offers parts kits for all of his boards. I suggest getting them to save you time and money, as his parts prices are as good as his board prices. This package is an entire system. It is well thought out and priced in the ZX users pocket book range. It is nice to see this type of expertise available in this price range for Timex Sinclair users. We will update this system from time to time as the boards go into service. Watch for major articles by John Oliger. They will be forthcoming, somewhere. Thanks John.