HP Vectra Technical Reference Manual page 241

7.4 Parallel Port Driver (lNT 17H)
The parallel port driver provides several functions that support data transfer on the parallel ports
and return status. These functions implement the features of the industry standard INT 17H
driver and the EX-BIOS extended functions. The EX-BIOS functions implement features not found
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in the industry standard functions, such as block (multi-byte) data transfer.
The following is a list of descriptions for each of the INT 17H functions. A summary of these
functions is shown in table 7.7.
Table 7.7
Parallel Port Driver Function Code Summary
INT
Function Function
Hex Equate Value Definition
17H INT_PRINTER Printer
F17_PUT_CHAR
OOH
Send printer one byte
F17_INIT
01H
Initialize printer port
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F17_STATUS
02H
Get printer port status
F17_INQUIRE
6FOOH
EX-BIOS present
F17_PUT_BUFFER
6F02H
Write a buffer to printer port
Parallel Port Driver Function Definitions
The following functions range check (between
a
and 3, inclusive) the requested port address
specified in the DX register. If legal, the function looks up the I/O address contained in the
STD-BIOS data area. If the port table entry is non-zero the port is assumed to exist. If the port
table entry is zero the function returns without altering any registers.
This function prints a character on the parallel port. Valid data is set up on the printer interface
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for at least 900 nanoseconds. If the BUSY signal indicates that the device is busy, it executes an
INT 15H function F15_DEV_BUSY. When it returns from F15_DEV_BUSY, the function waits
until the BUSY signal indicates the device is not busy. The function generates a 500 nanosecond
data strobe and holds the data valid for at least 900 nanoseconds. The function returns with the
port status in the AH register.
232 Serial and Parrallel I/O