It is an inherent problem with any user support group that a newbie does not receive the full benefit of prior activity. Obviously, a user who first shows up in April does not get to see the hardware/software demonstration given in March. And because the prior activities are thereafter “old hat” to the people who did participate in them, old subjects may never be raised again.
I was reminded of that recently when I set out to get disk drives for my 2068. I’ve never had anything except tape drives, so I’ve paid only the barest attention to disk-drive-related matters. But when I picked up an unused LarKen Disk Interface kit from a T/S enthusiast who never got around to trying it, I suddenly got VERY interested in the subject of the LarKen, only to discover that a basic discussion of what the system is, how you connect it up, and what it does, seemed to be missing from prior issues of this newsletter– no doubt “old hat” to most. What’s a newbie to do? So, for the benefit of future newbies, this article is a “beginners-eye review” of Larry Kenny’s LarKen Disk Interface system, with particular emphasis on set-up.
My first reaction on receiving the kit was– this is it??? While some LarKen systems may come with disk drives added by the prior owner, the basic kit simply has two smallish circuit boards, a rather-cheesy manual and a disk. Nothing else. The manual mentions almost casually that you also need a disk drive, power supply for the drive and a cable to connect everything up, but does not go into any detail on how this is done. Is connection really so easy, or is the manual deficient on that point?
It turns out to be just about that easy. External disk drive units, having their own power supplies in the case, are available in the used market for a variety of early computers. Some of these drives (e.g., Commodore and Atari) are “intelligent” peripherals and would not be a good choice for a LarKen system because they have been heavily modified for their particular use. But others, like those made for the Tandy/Radio Shack Color Computer (“CoCo”), are fairly generic disk drives that require a separate disk controller– which the LarKen provides. If you find an external unit housing a drive that meets your needs, you can use it as-is without getting into issues of power cabling and drive configuration at all.
However, if you need or want to replace the floppy drive that comes in an external case, that chore is not difficult. You have a wide choice of replacement drives available to you, since the LarKen will work not only with standard 5-1/4″ DSDD drives with 40 tracks per side (which probably has the greatest compatibility with other LarKen users) but also with older 5-1/4″ floppy mechanisms like 35-track per side drives, 80-track per side “quad-density” drives, and single sided instead of double sided drives, as well as 3-1/2″ drives. Luckily, most drives have standard power connectors and cable interfaces so an old drive can be taken out of an external case and an appropriate one configured and installed fairly easily with the same wiring. “Power splitters” are available from sources like Radio Shack if your external case has one full-height drive and you wish to replace it with two half-height drives (which typically use less power each). Power converters are also available if you want to put a 3-1/2″ drive in a space wired for 5-1/4″. If you uncover no external drive case to suit your needs, another possible power source is a computer power supply (inside its shielded case) removed from a junked PC or similar. Such unit likely has the disk drive power cables already in place and set to go. But of course, in that event, you’ll have to come up with a separate box to house the floppy drives.
Configuring a drive involves setting the drive to the number to which you wish it to respond. The LarKen refers to the drives it controls as “0” for the first one, “1” for the second, and so forth, and most floppy drives use the same designations (although you may run into some that use letters like “A” and “B”). Typically, there are two rows of pins somewhere on the drive circuit board with designations like “DS0” for drive 0 and “DS1” for drive 1, next to different pairs of pins. Look for a small slide-on connector tying a pair of pins together, and place that connector on the pair of pins next to the appropriate drive number. On older drives, you may find instead a configuration shunt, which will require you to cut the connections you do not need (e.g., for drive 0, cut the ones labeled 1, 2, & 3), or alternately, to reconnect up (with solder or wire) a previously-cut connection you do want. These older drives may also require a terminating resistor on the last (highest-numbered) drive; such resistor normally looks somewhat like a regular IC chip with 14 or 16 pins and has the resistor value written on it. So, if you take a pair of older drives out of another unit for this purpose, the one with the resistor will need to be the last drive, or the resistor will need to be pried out and relocated to the drive you want to be last.
The required interface cable, typically a ribbon cable with 34-pin Shugart-compatible female edge-card connectors on both ends, were common a few years ago and should not be hard to find. For instance, the CoCo cable, which is a flat cable without the “IBM Twist” in the middle (a segment of the wires twisted 180 degrees from how they would normally attach), will work. I did not test an “IBM Twist” cable.
In my situation, I removed a full-height 35 track drive from a CoCo external drive unit, and replaced it with two half-height 5-1/4″ DSDD 40-track models, utilizing a power splitter. I picked up those drives for about $5 apiece in a used software/hardware store; sometimes whole original PC-type computers can be found in the $10-$20 range and stripped of drives and any other appropriate parts. The new drives didn’t exactly fit the case like a hand in a glove (screw holes in wrong position and such), but they did go in, could be locked in place with a little electrical tape, and functioned fine.
As stated, two separate boards are needed by the LarKen system. One slides into the expansion port connector in the back of the 2068; that one, which has a pass-through interface for other peripherals and a 34-pin Shugart compatible card edge, is the actual disk interface to which your disk cable attaches. The other board goes into the 2068 cartridge port on top; this is the brains for the system, and avoids you having to load the operating system every time you turn on the computer. Command-wise, the LKDOS operating system makes your life is a bit more complicated because, when you wish to access the cartridge/drives, you are required to give a RAND USR 100: command (or a PRINT #4: command, if you have previously given a RAND USR 100: OPEN #4,”dd” command) preceding any disk instruction (e.g., RAND USR 100: LOAD “FILE.B1”). Giving such long commands can get old, but the right software can alleviate this (see LogiCall below).
With LKDOS alone, the system can LOAD, SAVE, rename files, erase files, give you a disk CATalogue, send the catalog to printer, and perform other simple tasks. Additional common disk-handling functions are done by separate programs. These extra utilities are what are on the LarKen System Disk, and include such things as formatting, copying whole disks if you have two drives, copying files from one drive to another, and copying files from one disk to another on a single drive (through “disk swapping”, which gets old fast since each program on the disk requires at least one and sometime more than one swap from source disk to destination disk and back again). These programs pretty well complete the list of basic disk handling functions, though different and additional utilities are available in T/SNUG’s LarKen Library if you want them.
But, as the old carnival barkers used to intone, “You say that’s not enough? You say you want more?” Well, the LarKen delivers more in additional features not strictly necessary to its basic mission. For instance, the system has built-in printer drivers that allow the LarKen to work with the AERCO, TASMAN and A&J parallel printer interfaces without loading extra code. It does NOT have built-in code to work with the Byte-Back parallel printer, and therein hangs a tale. I have (you guessed it) a Byte-Back parallel interface. The LarKen instructions state that you can load a separate parallel driver, tell the system where you placed it (with the appropriate POKE), and the system can use it. The cartridge even has some free RAM where you can stash the code and not use up any regular memory. Perhaps for some printer drivers this would be more than enough, but for reasons beyond what “read the manual” would solve, I am unable to successfully load and access the Byte-Back printer driver. I assumed there were lots of folks out there with LarKen/Byte Back systems who could advise me, but the LarKen experts I consulted had never run across this problem. I even dropped a note to David Leech, who is Mr. Byte-Back himself and a very helpful gentleman, but have not received a reply. If anyone KNOWS the solution (not “such-and-such OUGHT to work”), I’d still be interested. But in the meantime, the LarKen works well enough with my 2040 to print out disk catalogs and do other similar light-duty tasks.
The LarKen system supports the replacement of the 2068 ROM with a Spectrum ROM for running Spectrum software, or (with some minor hardware hacking) placing a Spectrum ROM on the interface in addition to the existing 2068 ROM (and here, Bob Swoger can supply you with the needed socket and ROM for $12, see his kind offer elsewhere in this newsletter). The system has a Kempston-style joystick interface, for use on those 2068 or (usually) Spectrum programs requiring Kempston joysticks. Perhaps most importantly, the interface has a “snapshot” feature that allows you to freeze a program in memory and save the image to disk. The primary use for this is moving to disk all those old cassette-based games that autorun.
I stated above that giving those long disk commands preceded by RAND USR 100: or PRINT #4: can get old after a while. I also noted the manual was a bit cheesy. Enter T/SNUG’s very own Bob Swoger, who both wrote his own LarKen auxiliary operating system called LogiCall, and rewrote the LarKen manual (which is bundled with LogiCall) to be clearer and more professional-looking. LogiCall, up to version 6.0 now, is a commercial program available for $15 from RMG or FWD Computing (see the ads elsewhere in this issue). A full review of LogiCall is beyond the scope of this article; a review of LogiCall 5.0/5.2 by Abed Kahale appeared in the Spring 94 issue of ZXir QLive Alive!, and Bob Swoger himself wrote a piece on LogiCall for the Fall 1996 issue. But suffice it to say here that it makes your life easier. You can arrange to autoload LogiCall by holding the ENTER button when you turn on the unit. (Actually, this autoload capability is built into LKDOS and is not unique to LogiCall, but LogiCall makes the best use of it.) LogiCall then presents you with a disk menu; you can move to get a menu from another drive with a single keystroke. The system allows you to load the program you want by typing in the name or cursoring down to it; and, you can perform many disk functions (like renaming, getting a disk CATalogue, or erasing) right from the menu with a couple of keystrokes. The software makes calls to certain utilities particularly easy, and even integrates a number of application programs (like Tasword Two and Vu-File) into the LogiCall system so that you may return to the LogiCall menu after exiting such programs without resetting the computer. Abed indicated in his article that using LogiCall was like upgrading from a gear-shift to an automatic with overdrive, and the analogy is useful. Perhaps more precisely, it feels like upgrading from a disk system which is a functional but somewhat awkward add-on to a computer not really designed for disk usage, to a system in which the drives are integrated so well that they appear to have been part of the system from the start. I would definitely recommend the LogiCall software.
Incidentally, LogiCall provides a clue about how to set up your 2068 system to achieve maximum text readability: it automatically changes the video display to light letters on a dark background, the opposite of normal. As you likely know from experience, a light screen tends to be overrun with what Fred Blechman’s “The Timex Sinclair 2068 Beginner/Intermediate Guide” refers to as the “crawlies”, being “wiggle lines that pervade the picture and are particularly noticeable on boundaries between colors.” TVs show a lot of crawlies, and monitors aren’t much better. Worse, color displays of any kind– TVs or monitors– can also show color bleeding and other color side effects that hurt text clarity. My suggestion is to follow LogiCall’s lead as far as it will go by finding a monitor that is monochrome composite (sometimes called “black and white” although usually green or amber on black). These things are practically being given away ($5-$10) when you run into them at garage sales and similar locales. By going light text on dark (which can be done with the appropriate PAPER. INK and BORDER commands if you do not have LogiCall), and by turning down the brightness on the monitor until the background is completely black, you can get sharp, readable text with an absolute minimum of crawlies and no color bleeding. You will especially appreciate this if/when you go into Display Mode 2 (64 column text) to use Tasword Two or other text applications. I would recommend in particular one of the old Zenith Data Systems monitors, which have a “40-80” switch on back. The “40” setting gives you a normal picture, while the “80” setting widens the aspect ratio of the picture, making those tall & thin 64 column characters fill out a bit more for better viewing. This is a FAR better situation video-wise than having to squint to tell a “w” from a “u” while crawlies and color bleeding run wild across your screen.
Several other types of disk interfaces are available for T/S systems. In the same Spring 94 issue mentioned above is information from The John Oliger Company (see ad elsewhere in this issue) as to “why the Oliger disk I/F with JLO Safe is the best available for your TS-2068”. AERCO, Ramex, and Zebra (TOS) are other choices you may run into in the used market. Not having any of these others, I cannot offer a comparison. But I can state that the LarKen (particularly mated with LogiCall) offers a number of convenient features and works quite reliably. It would not be a bad choice for any 2068 owner.