HP Vectra Technical Reference Manual page 230

The parallel printer port driver checks the status of the port before it outputs a character to
determine if the printer is busy. To prevent an error condition on the parallel port from hanging
up the system, a timeout loop is used. The length of the timeout is determined by the values
stored in the timeout table. The timeout values for each of the parallel ports can be set
independently of each other.
7.2.3 Print Screen Driver Data Structures
The print screen driver uses a single byte data structure, located at 0040:01 OOH (see Appendix
B). The print screen driver places a status byte at this location, indicating whether or not a print
screen operation is underway.
ThE~
possible values for this status byte are:
Data Definition
o
The print screen driver has not been called or it completed the previous
operation successfully.
1 Printing is in progress.
OFFH
Error occurred during printing.
If this byte indicates a print screen operation is currently in progress, the driver will return. This
prevents more than one print screen operation from occurring at the same time.
7.3 Serial Port Driver (lNT 14H)
The functions supported by the serial port driver can be divided into two groups; those that set
and report communication protocol or status, and those that transmit and receive data. The
driver supports nine functions. Four of these functions implement the features of the industry
standard INT 14H driver. The remaining five functions are
EX-BIOS
extensions. The
ROM BIOS
supports several features not found in the industry standard INT 14H driver. Among these
features is the ability to select a communication speed of up to 19.2
K
baud per second and the
support of block (multi-byte) data transfer.
The following is a list of descriptions for each of the INT 14H functions. A summary of these
functions is shown in table 7.4.
Serial and Parrallell/O 221