per
Veteran Member
There are several IBM cards with jumpers, and many of them is not even documented. Some got hints (like why exactly I/O address 278h-27Fh are reserved in the TechRef), but some aren't even mentioned in the schematics (talking of P3 of the CGA card).
I'll write the ones I figured out so far:
IBM Printer adapter, J1 (I/O address select):
Shorted = I/O address 378h - 37Fh
Seperated = I/O address 278h - 27Fh
This jumper doesn't really do anything since it is permanently shorted by a line on the PCB. To take use of it, you have to manually and carefully cut the line with a finer tool (chainsaw doesn't work) and solder in a 2-pin header on the jumper pad.
IBM Color Graphics adapter, P3 (Font select):
Shorted = Thin font
*Seperated = Thick font
On some cards, the headers for this jumper are missing. To use this feautre, solder in a 2-pin header on the jumper pad.
IBM Monochrome Display adapter, J1 (Unknown):
Shorted = Select the CGA font but disables the clock signal
*Seperated = Normal operation
I really don't know too mutch about this jumper. Might have been implemented before they decided to build the CGA as a standalone adapter instead of including it in the MDA design.
IBM Async. adapter, J1 (XT Slot 8 compability):
*Shorted = Operates in Slot 8 of the XT
Seperated = Does not operate in Slot 8 of the XT
Haven't tested how well it works in anything else than slot 8 with the jumper installed.
IBM 5 1/4" Floppy Disk Drive adapter (Clock enable):
*Shorted = Clock enabled
Seperated = Clock disabled
I really don't understnd why this jumper is included, as the adapter wouldn't problably work without it.
I'll write the ones I figured out so far:
IBM Printer adapter, J1 (I/O address select):
Shorted = I/O address 378h - 37Fh
Seperated = I/O address 278h - 27Fh
This jumper doesn't really do anything since it is permanently shorted by a line on the PCB. To take use of it, you have to manually and carefully cut the line with a finer tool (chainsaw doesn't work) and solder in a 2-pin header on the jumper pad.
IBM Color Graphics adapter, P3 (Font select):
Shorted = Thin font
*Seperated = Thick font
On some cards, the headers for this jumper are missing. To use this feautre, solder in a 2-pin header on the jumper pad.
IBM Monochrome Display adapter, J1 (Unknown):
Shorted = Select the CGA font but disables the clock signal
*Seperated = Normal operation
I really don't know too mutch about this jumper. Might have been implemented before they decided to build the CGA as a standalone adapter instead of including it in the MDA design.
IBM Async. adapter, J1 (XT Slot 8 compability):
*Shorted = Operates in Slot 8 of the XT
Seperated = Does not operate in Slot 8 of the XT
Haven't tested how well it works in anything else than slot 8 with the jumper installed.
IBM 5 1/4" Floppy Disk Drive adapter (Clock enable):
*Shorted = Clock enabled
Seperated = Clock disabled
I really don't understnd why this jumper is included, as the adapter wouldn't problably work without it.
