HP Vectra Technical Reference Manual page 228

7.1.3 Polled and Interrupt Driven Operations
Both the serial and parallel ports on the system may be operated in either a polled or interrupt
mode. The drivers in the ROM BIOS only support polled operation. Four system interrupts, OBH,
OCH, 72H and 73H, are reserved for system serial ports. Two system interrupts, ODH and OFH,
are reserved for system printers. Application programs and system software may use these
interrupts to operate the ports in an interrupt mode.
7.2 Data Structures
The data structures for the serial port, parallel port, and print screen drivers are located in the
5TD-B105 data area. The data structures for each of the drivers are discussed separately.
7.2.1 Serial Port Driver Data Structures
The serial port driver uses two data structures in the 5TD-B105 data area; a base port address
table, and a timeout counter table. The addresses of these data structures are listed in table 7.2.
The equipment word in the 5TD-8105 data area (40: 1 OH), contains the number of serial and
parallel ports configured in the system. The equipment byte can be read by the INT 11 H
equipment determination function.
Table 7.2
Serial Port Data Structures
Port Port Address Timeout Timeout
Number Table Entry
Table Entry
(Default)
0
40:00H
40:7CH
(01 H)
1
40:02H 40:7DH
(01 H)
2
40:04H 40:7EH
(01 H)
3
40:06H 40:7FH
(01 H)
Serial and Parrallell/O 219