PCjr Options and Accessories

Like other 8088 class machines, PCjrs did not keep time while they were turned off. There were many clock/calendar solutions for the Jr, usually packaged along with other things in a sidecar. One of the more unique clock/calendar solutions was this cartridge sold by Integrity Technology. Cartridges are 'read-only' on a PCjr because there is no write circuitry, yet you can set the date and time on this cartridge. The trick is in the Dallas Semiconductor DS1215 chip, which makes up the heart of the cartridge. (Read about the trick here.)

Have you found that two cartridge slots are not enough? Have no fear! This adapter turned one cartridge slot into two. As long as none of the cartridges you were using conflicted, it didn't really matter how many you put on a system.

Want to make a cartridge of your own design?

For a while something like this was fairly scarce. In the past few years it has become much easier to design and order custom circuit boards, so now you can find blank cartridge kits on eBay, Tindie, and other retro-recomputing friendly places.

The Keytronic KB5150jr keyboard is a great replacement for the PCjr keyboard but it doesn't have the infra-red communication feature so it must always use it's keyboard cord. It features Numlock and Capslock lights, which are managed by the keyboard. The PCjr has no way to tell the keyboard if the lights should be on or off, so if a program sets the Numlock or Capslock it is possible for the keyboard to get out of sync with the computer.

Unfortunately, this keyboard is not 'clicky' like the IBM PC keyboard using the buckling spring mechanism. It's rather mushy, and it's probably based on foam inserts under each key. The original foam inserts all rotted, but you can find replacements at Texelec.com.

The Keytronic KB5151jr features a separate cursor pad which is activated and deactivated using a dedicated key. Although it resembles an extended keyboard, it is missing F11 and F12, as these had not been introduced by IBM yet. Like the KB5150jr the keyboard features indicator lights for Numlock and Capslock. It also uses foam inserts under each key, giving it a rather mushy feel. Early versions of this keyboard had a bug in them that would cause confusion between the numeric keypad and the cursor keypad. Keytronic provided an upgraded EPROM that eliminated the bug. If you have one of these keyboards and it doesn't have this bug, please contact me - I need a copy of this EPROM to fix my KB5151jr!

This keyboard uses the same foam inserts as the KB5150jr so if you find one of these you'll probably need to replace those.

The documentation for this can be found here.

Here is an add-on numeric keypad for the PCjr. It is designed to be used with the original PCjr keyboard.

The documentation for this can be found here.

This little device sat between the diskette drive controller and the first diskette drive, altering some of the signals so that a second diskette drive could be added. It used the modem slot to draw power, and perhaps to snoop on some signals. (I need to analyze the wiring to find out exactly what it is doing.)

The second drive was usually located outside of the PCjr in a stand-alone enclosure with its own power supply. One interesting little side-effect of this card is that both drives would spin when one was accessed. Unlike the Racore expansion units, this did not have enough wiring or circuitry to control the drive motors independently.

The documentation for this can be found here.

There is a little known hack on the original PC CGA card that allows one to alter the font that is displayed. The card has two fonts on board, a 'single dot' and a 'double dot' font. These fonts each take up 2KB, and are stored in a 4KB ROM module on the card. The 'double dot' font is normally used, but if you alter the card slightly you can change it to use the 'single dot' font.

The Thin-Font module performs a similar trick for the PCjr. The PCjr font ROM only has the 'double dot' font. This replacement EPROM has both fonts in it. You can switch between the fonts by either using a toggle switch or by using the micro-clip and the included software. (The micro-clip would be attached to the output of a chip that could be controlled via software.)

Many people found the 'single dot' font to be more readable on the PCjr monitor. This upgrade was fairly cheap and easy to do.

The documentation for this can be found here.

The misspelling is theirs not mine - it's printed that way right on the card. This little beauty lets you plug 8 bit ISA cards into the sidecar bus of your PCjr. This is not for the weak of heart, and there are some restrictions:

• The card can not use DMA.
• The card is restricted to the available IRQs on the PCjr.

Using this adapter I have run a Trantor T130B SCSI card with a SCSI hard disk, A Future Domain 8xx series card with a SCSI hard disk, and various 8 bit Ethernet cards.

A pinout can be found at pcjr_isa_adapter.html. (I'm looking to recreate this adapter using KiCAD.)

The Koala Pad is an old school classic. It connects to the PCjr via a joystick port, and allows you to draw in a more natural way than a mouse or joystick allow.

The One Card is very similar to the jrHotshot. To install it you pry up the diskette drive tray, which reveals the 8088 CPU on the motherboard. You then very gingerly remove the original CPU and replace it with this board, which becomes a daughterboard to the motherboard. Room under the diskette drive tray is tight, so this this board has a fairly low profile.

Unlike other boards, this board has the 8088 soldered onto it, so you do not reuse your existing CPU. This also makes an upgrade to a V20 not feasible, unless you are very good with a soldering iron and willing to take some risks.

Solutions like this avoided a sidecar on the side of the system, but they put more of a load on the internal power supply and heated things up a bit.