Registers; Accessible Registers - HP Vectra Reference Manual

Registers
The card has three programmable registers that control the
operation of the parallel portion of the card. The system
programmer may gain access or control any of the registers in the
parallel adapter through the 80286. The registers must be
addnessed before a read or write operation can take place. The
following table defines the registers and their addresses.
Table 11.7
Accessible Registers
Address*
Hex Register
X78 or X7C Data Buffer Register
X7A or X7E Printer Control Register
X79 or X7D Printer Status Register
Data Buffer Register (X78H or X7CH)
This register contains the data character. Reading from this
address causes the character to be read by the card. Writing to
this address causes the character to be transmitted via the parallel
connector.
*The X is substituted with the appropriate port selection number,
a 3 for port 1, a 2 for port 2.
Serial/Parallel Card 137