This unit provides a parallel port that the PC JR did not supply on the main unit.
This allowed users to interface to the readily available impact printers, such as MicroLine, Okidata and others..
Soon after they were introduced the Jr folks found a way to make the board Bi-Directional with a few tweaks.
Below are some pictures of this board mod.
One of the uses that may Jr folks found useful was the addition of the ZIP drives, ie. ZIP-100 flavor.
Klaus Peichl was the author of the PALMZIP driver that is STILL available at his site for use with the JR.
Support Klaus if you plan to upgrade to a ZIP drive and buy a license from him, it is reasonable and supports his efforts.
http://leute.server.de/peichl/main.htm
Shown is the Par Port board with the Bi-Directional mod done.
Note the blue wire is attached from chips:
PIN-15 ZM11 SN74LS174
to
PIN-1 ZM4 SN74LS374
BLUE WIRE ADDED TO COMPLETE THE MOD

BLUE WIRE SHOWN ON BOARD DRAWING PIN TO PIN FOR CLARITY

BLUE WIRE UP CLOSE VIEW

UP CLOSE VIEW, ZM4-PIN1,
HOW TO :
Use flux for best solder flow. And do not heat up the chip pins any more than needed. Rule of thumb, 'get in and get out '

Using a solder sucker or solder wick, remove as much of the solder from PIN-1 on the back side of the board as you can.
If you need to do some touch up on the top side with wick do so.
Before you cut the pin, you must remove the solder the best you can, leaving the solder may damage the board via. and traces.
Using some side cutters, small flavor, place the flat side of the cutters to the board and gently with the tip of the cutters
cut the pin at that point.
You should be able now to, on the back side of the board, using tweezers, grab the pin, heat it up with the solder iron and pull it out gently.
If it resists check your cut or allow the solder iron to heat it up properly to melt the holding solder, USE FLUX.
Gently bend the cut pin up and away from the board lifting is slightly ( see the picture ).
You are ready to tack solder a length of wire (28awg is good) to the pin.
See the picture for the example. If you pre-tin the pin with a small amount of solder and wet the tip of the wire in flux, then hold it
on the pin and touch it with your solder iron it should quickly flow and attach the wire, again, 'get in and get out'.

UP CLOSE VIEW, ZM11-PIN15,
Using the same technique as above do ZM11 pin15 in the same manner and connect the other side of wire to that pin.
You are done.
Now just install your side car and test !

Use this file, written by Klaus Peichl to test your parallel port. ( again support Klaus )
Example output of LPT_TEST:
LPT_TEST 0.2 (c) 1998 by Klaus Peichl
---------------------------------------
Parallel port info utility.
Parallel port: LPT1
Port address: 0378
Readback after output: OK
Bidirectional capability: OK, Input=Low!
https://www.pcjribm.com/pcjrfiles/lpt_test.com