IEEE 488 Introduction
PSI BOX Reference
A typical example of a talker is a disk drive sending data,
a digital voltmeter sending data, a programmable oscilloscope
sending data, etc. There can be only one active talker on the
IEEE bus at any one time. When a device is commanded to talk
all other talkers are automatically commanded to untalk.
The Controller.
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A controller is a device that can instruct other devices to
talk or to listen. In addition, the controller can send interface
messages to command specified actions within other devices. A
typical example of a controller is your PC with the PSI BOX
connected, the PSI BOX can also act as a listener or a talker
when necessary.
The Controller In Charge.
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If there are several controllers present on the IEEE bus
only one of them at a time can be the Controller In Charge.
When a controller is not the Controller In Charge it must be in
the controller idle state. The Controller In Charge can be in the
controller standby state or by asserting ATN true, it is the Active
Controller. So the Controller In Charge at will can move
between the Active Controller and the controller standby states.
If several controller are connected to one bus then only
one of these can be the System Controller.
The System Controller.
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Whilst any idle controller can be instructed to become the
Active Controller only the System Controller can MAKE
ITSELF the Active Controller at any time. Only the System
Controller can assert the IFC and REN lines.
The PSI BOX can also act as controller in standby state, as
Controller in Charge or as System Controller.
The PSI BOX, in Mode 7, powers up as System
Chapter 2
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