Chapter 11: Hp-Il Interfacing; What You'lllearn In This Chapter; An Overview Of Hp-Il - HP 7470A Interfacing And Programming Manual

Chapter
HP-IL Interfacing
What You'llLearn in This Chapter
This chapter is only for 7470 owners with an HP-IL interface. HP 7470s
with Option 003 have an HP-IL interface.
In this chapter, you will find a brief overview of HP-IL, a list of the
HP-IL capabilities implemented on the 7470, and examples of sending
and receiving data using a variety of computers.
An Overview of HP-IL
In an HP-IL system, devices are connected to each other in a closed
loop. All devices communicate by sending messages consisting of 11
bits each; these messages travel through the loop in one direction, one
bit at a time. Only one message is traveling around the loop at a given
time.
There are three categories that describe whether devices can send or
receive messages: talkers, listeners, and controllers.
0 Talkers are devices that send data over the interface; only one talker
can be active at a given time. The controller designates the role of
talker with commands that are dependent on the specific controller.
The 7470is capable of being a talker.
0 Listeners are devices that receive data from a talker or commands
from a controller; several listeners can be active simultaneously. As
with talkers, listeners are designated by the controller. The 7470 is
capable of being a listener.
0 Controllers are in charge of all loop operations. For example, the
controller assigns the roles of talker and listener, assigns addresses,
and initiates data transfer between devices. There can be more than
one controller in a loop, but only one can be active at any time, and
only one can be the system controller. A controller is typically a
portable computer or calculator. The 7470does not have the ability to
be a controller.
HP-IL INTERFACING 11-1