The Standard Parallel Port (SPP) Adapter board allows to use the GPIO port of the 68k-MBC as a standard printer parallel port.
In this way you can use a legacy parallel (Centronics) printer.
To connect the SPP Adapter board to the GPIO connector of the 68k-MBC board you need a 10cm long 20 wires flat cable terminated with an IDC connector at both sides (pay attention to connect the cable in the right way on both sides, so the pin 1 on the 68k-MBC GPIO connector corresponds to the pin 1 on the SPP Adapter board GPIO connector).
Please note that you have to power off the 68k-MBC board before connecting or disconnecting the SPP Adapter board to it.
NOTE: before using the SPP Adapter board (A240721-R270921) you have to update both the IOS firmware and the SD image to the latest available version (see the FILES section).

The cable to use for the printer is the common parallel printer cable, with a DB-25 connector at one side and a Centronics connector at the other:

In the FILES section you can find a zip file with all the documentation needed to build the SPP Adapter board, including the Gerber files for the PCB production.

To enable the SPP Adapter board under CP/M-68K I've added on the drive B: the custom utility SPP.68K (and the source SPP.BAS).
You have to execute the SPP utility to enable the SPP Adapter board and “link” to it the LPT: CP/M device inside CP/M-68K. After the execution of the SPP utility the GPIO port will be linked and reserved (the “normal” GPIO opcodes/functions inside IOS will be disabled) to the SPP parallel port emulation until a system reset or reboot:

After the execution of the SPP utility you need to link the LST: logical device to the LPT: device with the CP/M command STAT LST:=LPT:

At this point you have a working printer parallel port on LST:, so if you give the Ctrl-P command all the console output will be echoed to the printer:

NOTE: The SPP utility will output an error message if the GPE (GPIO Expansion) option is not installed.

I've added a couple of source examples in the SD image (/gcc-68k/workdir directory) to show how to use the SPP Adapter with the gcc cross compiler.
The two source examples are getStatusSPP.c and writeTestSPP.c, and they are the ones I used for the first test of the SSP Adapter board:

I've prepared an “easy” link to get a small lot (5 pcs minimum) of PCB of the SPP Adapter. The link is this one.

If you are looking for a kit with all the needed parts or an assembled unit ready to use now there is a professional seller that can sell both and ship worldwide.
The link to the seller is this one.

All the project files are licensed under GPL v3.

Schematic.
A240721-R270921_SCH.pdf.

PCB Assembling Guide.
A240721-R270921_assembling_guide.zip.

BOM file.
A240721-R270921_BOM_v1.ods.

PCB Gerber files.
A240721-R270921_Gerber.zip.