Over-Clocking

The stock 200LX contains two clock crystals, one for the CPU and one for the Real Time Clock. The one that runs the CPU runs at just over 15MHz, but it’s frequency divided so the CPU actually runs at roughly 7.5MHz. Mind-bogglingly slow by today’s standards, but pretty darn fast for a 1996 PC XT that you can fit in your pocket.

As usual though, more speed is better, and the 200LX is no exception. This is, IMHO, a relatively simple over-clocking procedure. It is simply a crystal swap and then adding a TSR program (Terminate and Stay Resident). The reason that we need the TSR program is that the CPU clock also controls signalling to the LCD screen. At double-speed, the CPU and other processes run just fine, but the signal to the screen can vary between mildly skewed to completely unreadable. The TSR program simply does some magic with the screen controls so that the display looks correct.

The only aspect of this overclock which is slightly troublesome is that the crystal size used in the 200LX is not the usual rectangular can. It’s a tiny cylindrical can that looks exactly like a 32kHz watch crystal. These small size crystals seem to be hard to find in anything other than the 32kHz watch speed. They are out there, you just have to hunt for them.

The other thing that has to be kept in mind is that the stock crystal is just under 16MHz… so a 32MHz replacement is actually a bit faster than 2x. This is important because there are two different TSR programs for fixing the screen – one for exactly doubled crystals, and one for 32MHz crystals. The 32MHz ones are cheaper because they are appearantly a stocked or more-commonly available crystal. I’m using a 32MHz crystal myself and have not had any trouble with it, ever, so I don’t know what the advantage is to getting the more expensive one.

Performing the actual overclock is quite easy, for anyone with advanced soldering skills. Just unsolder and remove the existing crystal, then solder in the new one. Of course, first back up your HP 200LX to a memory card etc, and have your memory card ready to go with the TSR program preloaded, so when you put your 200LX back together and reboot, you can fix the screen skew right away.

Memory Upgrades

The stock 200LX was available initially with 1MB, then 2MB, and finaly as high as 4MB. The 1MB unit was, IMHO, kind of useless. 2MB is really the minimum. The reason is this: The memory in the 200LX is divided between your actual system RAM and your ‘hard drive’… in other words, the 200LX uses its memory as a RAM-Disk. So if you have just the 1MB unit, and you allocate 640kB to DOS, that leaves less than 400kB for use as your C:\ drive — enough for some basic PIM info, such as some phone contacts and appointments, but that’s about it.

Not surprisingly, expanding the 200LX memory was always an important matter. Upgrades are available in sizes from 2MB up to 96MB. You can plug in a 2MB or 4MB daughter-card, for the quickest and simplest upgrade. 8MB and upwards, required soldering and wiring, in order to access additional address lines from the CPU. And the 64MB and 96MB upgrades required further partitioning, into 2 or more RAM-Disks.

Personally, my 200LX is an 8MB unit and I’ve never used more than 3MB. I’d be fine with a 4MB unit. For what I use it for, I can’t see myself ever needing to get into the double-digits of memory. However, I know there are power-users out there that do make full use of their 200LXes and that need all the power and storage space that they can get.

Back-Lighting, Front-Lighting Solutions

The only real technical hindrance to the 200LX is the lack of any kind of supplemental lighting for the screen. The stock screen is fairly good as far as contrast and reflectivity, and will work in somewhat low light. But in the dark, or near-dark, forget it.

Several front-lighting solutions have been devised including ones that used the serial port for powering a LED on a wire. A true Backlighting solution has been devised in recent years, but requires a very high level of skill to install, and is not without risks.

As much as a backlit 200LX would be nice, I have decided it is not worth the cost and the risk. For me, I will stick with my stock screen and simply not use it in the dark.

Blinky Light

Unbelievable – two years now, and still no blinky light. I know how to do it – drive it off the serial port, just like I did on the Newton. So why haven’t I done it?

Well… for one thing I’ve been too busy using my 200LX to tinker around with it. For another, I’ve got lots of other blinky lights to amuse myself with — including some truly dangerous ones. So I don’t really need one on my 200LX.

So, I won’t say that I’ll never do it… but it’s not planned for any time soon. Maybe when/if my current 200LX finaly falls apart and I have to set up a new one, I’ll revisit the blinky light modification.