TwinPort Jr.: Cartridge port doubler for PCjr.

Not enough ports? Make two ports out of one using this!

  •  TwinPort JR (assembled)
  •  TwinPort JR (assembled)
  •  TwinPort JR (assembled)
  •  Example use
  •  Example use
  •  DIY Kit version
  •  DIY Kit version


The PCjr has two cartridge ports, but in some cases it is not enough!

For instance, our resetJR module uses one port. But then, what if you also wish to use our SDCart JR card reader and an accelerator cartridge?

Another use case is for software development, for instance to use a ZIF socket on an EPROM cartridge. Or even hardware development. For instance, when you need to probe a signals on your custom cartridge-based peripheral it is much easier with the board fully outside the PCjr slot.

If one of the above situations apply to you, or for any other reason why you need more than two ports, consider the TwinPort Jr.! It should be functionally equivalent to the Synectics Siamese Adapter.

  • Beveled card edge connector
  • Dual 36-pin card slots wired in parallel.
  • Available in ready-to use (assembled) and DIY versions (not assembled)

When using multiple cartridges, make sure there are no bus conflicts by reviewing which address range/chip selects are used by your cartridges before use!

We recommend turning the power off before inserting/removing cartridges.

Be careful not to short the exposed pins with anything (rings, etc) when in use.


Buy here

In stock : Ships within 5 business days unless noted otherwise (out of stock, pre-order, holidays, etc).
DescriptionTwinPort Jr., DIY Kit version (non-assembled)
product picture
DescriptionTwinPort Jr., pre-assembled version (ready to use)
product picture

We normally ship within 5 days (excluding week-ends and holidays) after payment.
Prices are in US dollars and are subject to change without notice.

Related products

Product photo

Insert this small module into one of the cartridge slots to easily add a power led and reset button to your system.


Product photo

This cartridge PCB lets you use MMC/SD cards as a removable storage medium for your PCjr and can even replace a hard drive!

Starting from $35.99

Product photo

PCB for making your own IBM PCjr computer cartridge.


(Volume pricing available)