Parallel Polling - HP 9000 Series 300 Tutorials Manual

Thus, the Active Controller responds to SRQ by:
• Conducting a serial poll of individual devices on the bus,
• Conducting a parallel poll of return data lines to determine which line
is being asserted, or
• Conducting a parallel poll to identify the asserted data line followed by
a serial poll of devices programmed to assert that line when SRQ is
being asserted by the same device.
HP-IB parallel and serial polls are conducted by the DIL subroutines
hpib_ppoll
and
hpib_spoll,
respectively. The next section explains how to
use these subroutines.
Parallel Polling
The parallel poll is the fastest means of determining which device needs service
when several devices are connected to the bus. Each device on the bus that
is capable of responding to parallel polls can be programmed to respond to
parallel polls by asserting a given data line, thus making it possible to obtain
the status of several devices in a single operation. If a given device responds to
the poll with a data line response (I need service), more information about its
specific status can be obtained by conducting a subsequent serial poll of that
device.
3-34 Controlling the HP-IB Interface