HP 340 Series Service Manual page 67

Each frame is a 150 J.lsec long, IS-bit fixed format. A frame is shown in Figure 3-7.
idle start command parity
state bit bit bit
+
+ + +
L
I
2
Old
~e.r-L..._O--L-I--L._7--L..-_6----1I_o ~ _ e . . . ! - y _ 1 _ d . l . . . - 1 a _ ~ - - 1 . . I _ b ~ _ t e . . L - 1
-----I_o---'-I-----JI
k-
10 uSee
per bit,
+/--
0.5%
Frame (150 uSee)
Figure 3-7. HP-HIL Frame Structure
t
stop
bit
idle
state
+
Frames may be sent as fast as once each 154 J-lsec allowing data transfer rates of up to 6500
bytes/second. HP-HIL protocol performs automatic configuration, identification, and polling
of up to seven devices. Error recovery, device and system reset, and simple output commands
provide a simple device integration.
VVhen the SPU is turned on, the link is polled for devices. Each device on the link has its own ID
which is sent to the SPU and stored in memory. The link is polled 60 times per second. Should
a device have data to input to the SPU, it sends its data frame to the SPU for processing. As
each device's fralnes 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 SPU.
Functional Description
55