Some of the most fun things about the PCjr are not the
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
When the PCjr was announced lots of companies jumped on
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
that were available for the PCjr. The more interesting
options are described later.
ROM patch to speed the boot process. Works
by skipping some of the memory testing the machine normally does on a
BIOS to make the machine
a PC. Can be used to run much software that previously
different BIOS patches in
Three versions were produced. Version 1.0 combines the
Buffer cartridge and the jrVideo cartridge. Version 2.0 adds
QuickSilver cartridge. Version 3.0 adds the Compatibility
dip switches on it that allow
you to set the
number of disk drives (up to four) and the video mode that the PCjr
up in. Also lets you change the 'ID' byte in ROM to make the
itself as a PC.
256KB to 1MB of memory to a
Jr. Memory above 736K is used for a ram disk.
sidecar adds Adlib and
sound to your Jr. Also implements the 'Tandy mod' without
soldering or other modification. Optionally includes the
a bus mouse, and either 128K or 256K of memory. (The memory
to bring the machine from 512 or 640K up to 736K.)
One of several
that let you use standard PC cards on a Jr
Muppet Learning Keys
A kids style
actually connects through the joystick port.
notes on the
various options ...
Enterprises Configuration Plus Cartridge
almost like a
Swiss Army knife:
One switch allows you to change the ID byte
to make it look like a PC instead of a PCjr.
Two switches let you set the number of
much like the switches on a PC or XT motherboard.
Two switches let you set the display type to
other than the default 40 column color display.
Three LEDs track the state of Scroll Lock,
Num Lock, as the machine reports it. Unlike the keyboards
this, the cartridge won't get out of sync with the machine. (It
requires a TSR to operate though.)
Demon Attack by Imagic is a classic "kill the aliens in space" game
originally released in 1982 for the Atari 2600 and ported to many other
machines, including the PCjr.
The PCjr version took advantage of the extra color and sound available
on the machine, making it competitive with the other machines that were
designed as game consoles. Space on the cartridge was limited so Imagic
did not implement a title screen - when the machine boots it goes right
into the demo mode of the game.
If you would like to see a sample of the graphics and the sound from
the game take a look at the YouTube video to the right.
Technology Clock Cartridge:
Like other 8088 class machines, PCjrs did not
while they were
turned off. There were many clock/calendar solutions for the
usually packaged along with other things in a sidecar. One of
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
the heart of the cartridge. (Email me and I'll tell you the
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.
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.
Blank Cartridge Kit:
Want to make a cartridge of your own design?
The Racore Keyboard
Adapter allowed you to use a full-sized PC or XT keyboard on the Jr.
You could also have your PCjr keyboard attached at the same
time, just in case you needed to switch back and forth between the two
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
It features Numlock and Capslock lights, which are managed by the
keyboard. The PCjr has no way to tell the keyboard if the
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
probably based on foam inserts under each key.
a separate cursor pad which is activated and deactivated using a
dedicated key. Although it resembles an extended keyboard, it
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,
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!
The Rapport and
solutions are related. I think that Rapport turned into
Racore. There are several variations of the product:
Early memory cards in the Rapport/Racore added
RAM to the system. There were sockets for 256KB more RAM,
would bring the daughter card in the expansion chassis to 384K, or 512K
for the entire system. Chips were 64KB x 1 bit chips,
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
The clock and calendar is provided by an OKI 5832 chip.
DMA is option on these units. Non-DMA units have a 24 pin
EPROM. The DMA versions have a 28 pin BIOS EPROM and the
Docs for the Rapport Drive 2 Model 1200 can be found here. The Racore and Quadram
units are similar.
Enterprises TMC 850Jr:
This is an amazing
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
sidecars that adds
a SCSI adapter to your Jr. This particular model is based on
popular Future Domain 950 chipset, which is a classic SCSI implemention
early 90s. The DOS drivers support hard drives, CDROMs, and
storage, and they seem to work on the Jr. With this adapter
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,
is borderline infuriating. (Later BIOS versions apparently
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
not. The thing that makes me think this is plausible is that
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
a PCjr to boot from this card.
Firmware Drive II:
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
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.
increases the clock speed of your PCjr from the standard 4.77Mhz to
9.54Mhz. You install it by removing the 8088 CPU under the
drive and replacing it with this board, which fits snugly under the
disk drive. (This is very similar to the Jr HotShot.) The
board comes with a NEC V20 which replaces the original 8088 CPU. The
board also has some memory configuration software on it
which can eliminate the need to run a device driver to recognize extra
There is a
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 IBM internal
(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
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:
This sidecar adds
capability to a
PCjr. It supports
CGA, EGA, and other display modes, and VGA up to 800x600 in 16 colors
is technically an SVGA mode. The sidecar comes with
the standard PCjr monitor and a standard VGA monitor. A
some BIOS modifications is required to make it work. Besides
the VGA card, the BIOS also eliminates the need for memory device
This might be one of
memory cards ever
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
stock 128K Jr and expand the conventional memory to 736K. (640K
the traditional limit, but the memory map on the Jr allows you to get
736K.) Then, you'll still have 416K of what they call 'PCE
which can be used as a RAM disk.
If you put it on a 640K Jr, it will bring conventional memory up to
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
window high in the memory map, and it uses a software driver to bank
the visible portion. PC Enterprises didn't initially offer a
driver, but they made one available later. The memory in this
does not get cleared by BIOS on a reboot, so if you were using it as a
disk the contents of the RAM disk would survive a reboot.
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
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.
The Koala Pad
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
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.
Created November 30th,
2001, Last updated August 24th, 2008
(C)opyright Michael B. Brutman, mbbrutman at gmail.com