PCjr Options and Accessories

Some of the most fun things about the PCjr are not the machine itself, but in all of the cool options that were made for it. The PCjr was kind of an oddball: limited expansion, cartridge slots, non-standard connectors, and sidecars. This means that many options for the PCjr are unlike anything else designed for the rest of PC family.

When the PCjr was announced lots of companies jumped on the bandwagon. IBM had been so successful with the IBM PC that anything it put its name on would be gold. Well, things didn't quite work out that way. You'll see some mainstream PC companies here like Quadram, Spinaker, Microsoft, Lotus, and AST. As the PCjr market fizzled out smaller companies such as PC Enterprises, Racore, and ES Quality Products moved in to fill the void. By 1986 PCjr products were definitely a niche market.

The following tables give you a partial list of the options that were available for the PCjr. The more interesting options are described later.

Cartridges (Utility):

Cartridges (Applications):

Cartridges (Games):

Cartridges (Educational):

Memory Expansion Sidecars:

Keyboard Enhancements:

Expansion Chassis:

Miscellaneous Internal Upgrades:

Miscellaneous Sidecars:

Other Accessories/Upgrades:

Some notes on the various options ...

PC Enterprises Configuration Plus Cartridge

This little gem is almost like a Swiss Army knife: One switch allows you to change the ID byte of the machine to make it look like a PC instead of a PCjr. Two switches let you set the number of diskette drives, much like the switches on a PC or XT motherboard. Two switches let you set the display type to something other than the default 40 column color display. Three LEDs track the state of Scroll Lock, Caps Lock and Num Lock, as the machine reports it. Unlike the keyboards that do this, the cartridge won't get out of sync with the machine. (It requires a TSR to operate though.)

River Raid, Pitfall II, and Demon Attack:

Integrity Technology Clock Cartridge:

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. (Email me and I'll tell you the trick.) If you need software to drive one of these drop me an email. I just recently (Jan 2006) wrote a small C program that can talk to this cartridge and set the DOS date and time accordingly.

Synectics Siamese Adapter:

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.

Integrity Blank Cartridge Kit:

Want to make a cartridge of your own design?

Racore Keyboard Adapter:

Keytronic KB5150jr:

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.

Keytronic KB5151jr:

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!

Keytronic KB5149jr:

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

Rapport/Racore Expansion Units:

Early memory cards in the Rapport/Racore added 128KB of RAM to the system. There were sockets for 256KB more RAM, which would bring the daughter card in the expansion chassis to 384K, or 512K for the entire system. Chips were 64KB x 1 bit chips, organized in groups of eight. (Remember, this system doesn't have parity memory.)

A later memory card has 512K on it, which brings the entire system up to 640KB.

The clock and calendar is provided by an OKI 5832 chip.

DMA is option on these units. Non-DMA units have a 24 pin BIOS EPROM. The DMA versions have a 28 pin BIOS EPROM and the extra DMA circuitry.

PC Enterprises TMC 850Jr:

This is an amazing sidecar. Very hard to find too. If you find one, don't let it go. If you do decide to let it go, talk to me first. :-)

The TMC 850Jr is one of two PC Enterprises designed sidecars that adds a SCSI adapter to your Jr. This particular model is based on the popular Future Domain 950 chipset, which is a classic SCSI implemention from the early 90s. The DOS drivers support hard drives, CDROMs, and removable storage, and they seem to work on the Jr. With this adapter on your PCjr you can boot directly from a SCSI hard drive.

The other model is based on the same chipset that Seagate used on their ST01 SCSI adapter. The ST01 chipset isn't as desirable; it's basically enough to boot a hard drive. And sometimes the BIOS extension that comes with the chipset is limited to boot only specific Seagate hard drives, which is borderline infuriating. (Later BIOS versions apparently removed this limitation.) I don't know of any ASPI drivers for the ST01 chipset, so a CD-ROM is probably out of the question.

If you do enough research using Google, there is some folklore out there that says the two chipsets are very similar, and that the difference between them is just a few bit mappings in some registers. I've never seen specific enough information on either chipset to know if this is true or not. The thing that makes me think this is plausible is that my specific TMC 850Jr adapter has "ST01JR" stenciled on the card.

On this card you will notice two EPROMs. One is for a ROM extension provided by PCE which includes some utilities available from the DOS prompt. The other EPROM is the ROM extension that allows a PCjr to boot from this card.

Creative Firmware Drive II:

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.

PC Enterprises jrExcellerator:

PC Enterprises Thin-Font:

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.

PC Enterprises 2400bps Internal Modem:

The IBM internal modem (made by Novation) was only 300bps, which was obsolete when the PCjr was announced, and not much fun to use. At a time when 'Hayes Compatible' meant everything, this modem was slow and had its own command set.

The PC Enterprises 2400bps used the same internal modem slot, but it was eight times faster and it was Hayes compatible.

PC Enterprises Display-Master:

PC Enterprises Megaboard:

The sidecar can hold up to one megabyte of memory. The memory is very flexible - if this is the only memory card on the system, it will take a stock 128K Jr and expand the conventional memory to 736K. (640K is the traditional limit, but the memory map on the Jr allows you to get to 736K.) Then, you'll still have 416K of what they call 'PCE memory' which can be used as a RAM disk.

If you put it on a 640K Jr, it will bring conventional memory up to 736K and the rest of the memory (928K) will be available as 'PCE memory'.

The 'PCE memory' is similar to EMS memory; it's accessed through a small window high in the memory map, and it uses a software driver to bank switch the visible portion. PC Enterprises didn't initially offer a true EMS driver, but they made one available later. The memory in this range does not get cleared by BIOS on a reboot, so if you were using it as a RAM disk the contents of the RAM disk would survive a reboot.

PCjr Buss Adapter:

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 at heart, and there are some restrictions: The card can not use DMA. The card is restricted to the available IRQs on the PCjr. I will make the pinout and schematic available when I get around to it. I basically have the pinouts from a different source - I just want to make sure they match the pinouts used on this adapter. 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.

Koala Pad:

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.

Legacy The One Card:

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.