| Legacy Technologies of Lincoln, Nebraska made a
series of expansion
units for the PCjr.
Two basic designs were available. The "Legacy"
series was an expansion
chassis that sat on top of the PCjr system unit. The Volksbox was
designed to stand alone away from the system unit. Both units connected
to the PCjr through the sidecar expansion bus on the right side of the
PCjr. Both units also featured the L-Bus expansion slots and
room for either a floppy drive or a hard drive.
There are two versions of the expansion chassis
that
sits on top of the PCjr. One version, featured at the right,
includes a front panel display known informally on other systems as
"blinkenlights." The other version (pictured below) is plain
with slots for
air circulation instead.
In early 1988 the basic "Legacy" expansion unit with a
70 watt power supply and no options cost $140. The "Legacy II" added a
floppy drive and a floppy drive controller and cost $349. The "Legacy
III" added a 20MB drive and controller card (but no floppy drive) and
cost $1095.
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Legacy III with a 20MB
hard drive installed |
L-Bus cards
| One of the unique features of the Legacy expansion
units was the
inclusion of a proprietary expansion bus they designed called the
"L-Bus" that could be used to add up to four cards in an expansion
unit. The L-Bus was an extension of the PCjr bus - it connected to the
sidecar expansion connector using a ribbon cable and terminated in a
small board with four expansion slots. The L-Bus
had 20 extra lines including 8 new data lines. In theory that would
allow for 16 bit data transfers within that part of the bus but no
cards took advantage of that
Expansion cards included a memory card, a clock/calendar
and parallel
printer port card, and a hard drive controller. All of these cards were
specific to this expansion unit - they were not industry standard in
any way.
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Legacy Technologies
memory card (256KB)
Memory
cards were available in 128KB and 256KB versions. A 512KB version was
planned but never delivered. In early 1988 the 128KB card sold for $119
and the 256KB card sold for $159. |
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Legacy Technologies
hard drive controller card
pair
Note that one card plugs into the L-Bus in the expansion unit
while the other card is attached to the underside of the hard drive.
The two are connected by a ribbon cable.
The first card has some address decode logic and the boot ROM that
allows the PCjr to boot from the hard drive without software drivers.
The second card is the actual hard drive controller. It is a Western
Digital WD1002-HDD. The drive that this particular card is
attached to is a Teac SD-520U. The controller is capable of controlling
up to three hard drives but due to the way the BIOS is written they all
have to be the same size and type. (You would also have to find a way
to install and power the additional drives; only one drive will fit in
an expansion chassis.)
In early 1988 the controller card set was selling for $595. |
Legacy Technologies
floppy drive controller
If your expansion chassis was populated with a
2nd floppy drive then
you needed a new floppy controller to replace the one inside of the
PCjr. This card was not an L-Bus card - it was a direct replacement for
the PCjr floppy drive controller. The card comes with a two position
floppy drive cable which has to be snaked up to the expansion
chassis. The Legacy floppy controller can
control two
drives but it does nothing to tell the BIOS of the machine that two
drives are installed - you still have to boot with a device driver to
patch the BIOS to recognize the second drive.
In early 1988 this controller was selling for $99. |
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"Blinkenlights"
Some of the Legacy expansion units were especially pretty -
they were blessed with a front panel worthy of a science fiction movie
from the 1950s. The lights were not just pretty - they could be used to
give you an idea of what the machine was doing. You could tell
if the machine was reading or writing memory, reading or writing
to
an I/O port, and what address was currently on the bus.
The address on the bus was shown in the lights
with the most significant bits of the address represented on the left
side of the display. All one megabyte of address space
available to the 8088 was shown. By looking at the lights you could
easily tell if the machine was operating out of ROM (high addresses) or
RAM
(lower addresses).
An improvement on the design would be to have a
'freeze' button to
latch and hold the LEDs on the display - the machine is updating at
4.77Mhz which makes it too fast for real debugging.
Below is a link to a video which shows the lights in
action during the
boot process:
Construction
The
expansion unit is a metal
case with options
for rear mounted port
connections and a cooling fan. Inside the expansion unit are a small
power supply, the L-Bus "motherboard", and a mounting bay for a 5.25"
hard drive or floppy drive. The power supply uses a standard
IEC C14
socket so that you can use a common line cord, not another external
PCjr power transformer like the Racore/Rapport expansion chassis use.
The
connection to the PCjr expansion bus is through the long ribbon cable
which traverses the chassis and drops down through a hollow side-car
connection. The connector on the ribbon cable that interfaces to the
PCjr is a standard IDC connector with no provision for a passthrough.
This means that you can not add additional sidecars once the cable is
in place. The choice of a long ribbon cable is interesting too -
usually they are avoided for system buses because of the potential for
problems related to noise.
The expansion unit sits directly on
top of the PCjr and is not attached in any way. If you make the mistake
of trying to pick the machine up from the expansion unit and not from
the PCjr itself, you will separate the two and possibly damage the
ribbon cable or connectors.
Compare this design to the Racore expansion chassis:
- The Racore uses a "double height" sidecar to
house electronics and provide a rigid connection between the PCjr and
the expansion chassis.
- The Racore uses printed circuit boards - there
is no ribbon cable.
- Additiona sidecars can be added after the
Racore is installed
- The Racore includes a parallel port and
clock/calendar. If the Racore is adding a second floppy it adds BIOS
support for the floppy.
In general the Racore expansion chassis products are better thought
out, but they are not perfect either. The Racore does not have
any sort of bus for adding additional
functions. The Racore also requires the use of a second PCjr external
power transformer.
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Besides these expansion units Legacy sold other upgrades for the PCjr,
including a memory upgrade that fit under the floppy drive and an 8087
math co-processor board. (That board also installed under the floppy
drive, so it could not be used with their memory expansion board that
also installed there.)
Legacy probably didn't sell too many of their expansion units - in the
11 years that I've been collecting and researching I have only come
across two samples, and I don't know of anybody else who has one. I've
also never come across the smaller Volksbox featured in their brochure.
If you own a Legacy please drop me a line and lets compare notes!
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