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Controller, this suits 99.99% of all users.
__________________ _
Controller Summary.
To sum up the Controller states.
1)
A controller commands other devices whether they should
talk, listen or perform some other action.
2)
To avoid confusion, if several controller are connected to
an IEEE system, only one of them at a time is allowed to
send commands to the bus. This is the Controller In
Charge.
3)
Interface messages exist for controllers to pass control
between each other, ie make each other the Controller In
Charge.
4)
Only one controller on an IEEE system can be the System
Controller. The System Controller has several unique
abilities. The System Controller alone can set the IFC and
REN signals true or false. The System Controller can make
itself the Controller In Charge, at any time, by sending the
IFC signal true for 100 micro seconds.
Command Mode And Data Mode.
_____________________________ _
Two type of messages may be transmitted on the IEEE
bus. These are device dependant messages and interface
messages. Device dependant messages are distinguished from
interface messages by the state of the ATN line.
The controller asserts ATN true when it wants to send an
interface message, the IEEE bus is said to be in COMMAND
MODE. When ATN is false the data on the data bus is a device
dependant message, the IEEE bus is said to be in DATA
MODE.
Only the Active Controller can send interface messages,
that is, commands.
Any active talker can send device dependant messages, that
is, data.
Page 18
IEEE 488 Introduction
Chapter 2
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