Parallel Portion Of The Adapter - IBM RT Series Hardware Reference Manual

Parallel Portion of the Adapter
The parallel portion of the adapter makes possible the attachment
of various devices that accept eight bits of parallel data at
standard TTL levels. The rear of the adapter has a 25-pin,
D-shell connector. This port may be addressed as either parallel
port 1 or 2. The port address is determined by the position of
jumper J2, as shown in the following figure.
Port 1
Serial/Parallel Adapter 19