Accepting Active Control - HP 9000 Series 300 Tutorials Manual

Accepting Active Control
Any Active Controller can pass control to any other device on the bus,
but only a Non-Active Controller can accept control. When an Active
Controller interface passes control to a Non-Active Controller interface, the
Non-Active interface automatically accepts control and the former Active
Controller becomes a Non-Active Controller. However, when this transfer
of control occurs, the interface receiving control does not automatically
notify the computer that control has been received unless the necessary
interrupts have been set up by the application program by use of subroutines
hpib_bus_status, hpib_status_wait, and io_on_interrupt.
hpib_status_wai t has been mentioned in previous discussions about the
Active Controller and System Controller. The following discussion provides a
look at its uses.
Call hpib_status_wai t as follows:
hpib_status_wait(eid. status);
where eid is the entity identifier for an open interface file and status is an
integer indicating what condition you want to wait for. The following values for
status are defined:
Value
WAIT_FOR_SRQ
WAIT _FOR_CONTROL
WAIT _FOR_TALKER
WAIT _FOR_LISTENER
Condition
Wait until the SRQ line is asserted
Wait until this computer is the Active Controller
Wait until this computer is addressed as a talker
Wait until this computer is addressed as a listener
Controlling the HP-IB Interface 3-65