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Legacy Technologies
PCjr Expansion


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.

Legacy Technologies expansion chassis

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.

Legacy Technologies L-Bus

Legacy Technologies memory card

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.
Legacy TEchnologies hard drive controller 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.
Legacy Technologies floppy controller


"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:

Legacy PCjr Blinkenlights
Closeup of the Legacy blinkenlights YouTube video of the Legacy in action


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.
Legacy Technologies expansion chassis bare
Legacy Technologies expansion connection



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!

Created in September 26th, 2009, Last updated June 19th, 2011
(C)opyright Michael B. Brutman, mbbrutman@yahoo.com

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