HP 330 Service Information Manual page 127

ILink Interface
Data is exchanged between the device and the host computer through the link interface. It
accepts commands from the microprocessor for transmitting and receiving messages in an HP-
HIL frame format.
Each frame is a 150 J-lsec long, 15-bit fixed format. A frame is shown in Figure 3-27.
idle start
st<Jte bit
+ +
command
bit
per bit,
+/-
0.5%
+
fig. 3-3.2
98561/90801/1 sm2_ d
parity idle
bit state
+
+
t
stop
bit
1 Frame (150 uSec)
- - - - - - . 1
Figure 3-27. HP-HIL Frame Structure
Frames m.ay be sent up to once each 154 sec allowing data transfer rates of up to 6500
bytes/second. HP-HIL protocol performs automatic configuration, identification, and polling
IOf up to seven devices. Error recovery, device and system reset, and simple output commands
provide a simple device integration.
When the computer is turned on, the link is polled for devices. Each device on the link has
its own ID which is sent to the computer and stored in memory. The link is polled 60 times
per second. Should a device have data to input to the computer, it sends its data frame to the
computer for processing. As each device's frames has its own address in a 3-bit word, no more
than 7 devices can be used on the link at one time.
HP-HIL Cables
A four-wire cable connects HP-HIL devices to each other and to the computer. AMP Shielded
Data Link (SDL) connectors are used and are easily installed and removed from the computer
or device. Keyboard cable connectors are keyed and are marked with dots to indicate where
they are connected. Figure 3-28 shows the connector pinouts.
0
0
+4
+2
+3 +1
Figure 3-28. HP-HIL Cable Connector
Functional Description
111