Passing Control; What If Control Is Not Accepted - HP 9000 Series 300 Tutorials Manual

Passing Control
The subroutine hpib_pass_ctl can be used to pass control of the bus from
the computer (which must be the current Active Controller) to a Non-Active
Controller. A Non-Active Controller is a device capable of becoming Active
Controller, which usually means it is another computer.
hpib_pass_ctl is called as follows:
hpib_pass_ctl(eid. address);
where eid is the entity identifier for an open interface file that is currently the
Active Controller and address is the bus address of a Non-Active Controller.
Upon completion, the Non-Active Controller becomes the new Active
Controller and the local interface is a Non-Active Controller.
While hpib_pass_ctl can pass active control capability, it cannot pass system
control capability.
What If Control Is Not Accepted?
Your program is not suspended if the Non-Active Controller that you address
does not accept active control of the bus, but the computer still loses active
control meaning that the bus no longer has an Active Controller. If this
happens, the computer must use its position as System Controller to assume
the role of Active Controller by executing hpib_abort (see System Controller·
Role section which follows) or io_reset.
No error is returned by hpib_pass_ctl if the device that you address does
not accept active control, and there is no direct way to determine in advance
whether a given device can accept active control. There is also no way for
the computer, after initiating hpib_pass_ctl, to determine whether active
control has been accepted. However, if the computer that has passed control
immediately requests service after passing control and detects a timeout before
the request is acknowledged, this indicates that active control may not have
been accepted.
Controlling the HP-IB Interface 3-49