Measurement Computing Micro 488/EX rev.2.1 - Manual (Page 36)

Section 3 IEEE Operating Modes
3.2
The state diagram below shows the relationships between the various operating
modes. The top half of the state diagram shows the two operating states of a System
Controller. At power on, it is the active controller. It directs the bus transfers by
sending the bus commands mentioned previously. It also has control of the Interface
Clear and Remote Enable bus lines. The System Controller can pulse Interface Clear to
reset all of the other bus devices.
As shown in the diagram, the System Controller can pass control to some other
bus device and thereby become a Peripheral to the new Active Controller. If the
System Controller receives control from the new Active Controller, then it will once
again become the Active Controller. The System Controller can also force the Active
Controller to relinquish control by asserting the Interface Clear signal.
Passes Control or
System Controller (SC)
Not System Controller (*SC)
Active
System
Controller
SC•CA
System
Controller,
Not Active
SC•*CA
Active
Controller,
Not System
Controller
*SC•CA
Peripheral,
Not System
Controller
*SC•*CA
Power On
Power On
Controller Active (CA) Peripheral (*CA)
Asserts Interface Clear
Passes Control
Detects Interface Clear
Receives Control
Receives Control or
IEEE Bus Operating Modes State Diagram