The Gpio Interface; Data Lines; Handshake Lines - HP 9000 Series 300 Tutorials Manual

Linking OIL Subroutines
The
Iibdvio.
a library redefines the read, write, fentl, dup, and ioetl entry
points. For DIL to work properly, the DIL library must be linked before
Ii
be.
The GPIO Interface
The GPIO (General Purpose Input/Output) interface is a very flexible parallel
interface that allows communication with a variety of devices. On Series 300
computers, the interface sends and receives up to 16 bits of data with a choice
of several handshake methods. External interrupt and user-definable signal
lines provide additional flexibility.
The GPIO interface is comprised of the following lines:
• 16 parallel data input lines
• 16 parallel data output lines
• 4 handshake lines
• 4 special-purpose lines.
Data Lines
There are 32 data lines: 16 for input and 16 for output. These lines normally
use negative logic (0 indicates true, 1 indicates false). The logic can be changed
so that a 1 indicates true with the interface's Option Switches. Refer to your
GPIO interface manual to see how to do this.
Handshake Lines
Although four lines fall into this group, only three are used for controlling the
transfer of data:
• PCTL-Peripheral ConTroL
• PFLG-Peripheral FLaG
• I/O-Input/Output.
A-2 Series 300 Dependencies