Jumper Descriptions - IBM RT Series Hardware Reference Manual

Jumper Descriptions
Located on the adapter are two jumpers designated PI and P3.
Jumper P I changes the function of pin 2 on the direct drive
interface. When placed on pins 2 and 3, jumper PI selects ground
as the function of direct drive interface, pin 2. This selection is
for displays that support five color outputs, such as the IBM
Color Display. When PI is placed on pins I and 2, red prime
output is placed on pin 2 of the direct drive interface connector.
This supports the IBM Enhanced Color Display, which utilizes six
color outputs on the direct drive interface.
Jumper P3 changes the I/O address port of the Enhanced
Graphics Adapter within the system. In its normal position, (pins
1 and 2), all Enhanced Graphics Adapter addresses are in the
range 3XX. Moving jumper P3 to pins 2 and 3 changes the
addresses to 2XX. Operation of the adapter in the 2XX mode is
not supported in BIOS.
The following figure shows the location of the jumpers and
numbering of the connectors.
IBM Enhanced Graphics Adapter 85