HP 9000 Series 300 Tutorials Manual page 96

by the Active Controller, uses internal configuration, or does not support
parallel poll.
To configure the parallel poll response for a given device by remote control
from the Active Controller, use the HP-IB command sequences PARALLEL
POLL CONFIGURE followed by PARALLEL POLL ENABLE. This
combination of two commands tells all devices currently addressed as listeners
to respond to any future parallel polls by asserting a specific data line with
a specific logic level. Most devices that do not support remote configuration
programming have internal configuration switches or jumpers that perform
an equivalent function but which cannot be changed remotely by the Active
Controller.
Devices that can be remotely configured can be programmed to respond with
a logic 0 or logic 1 level on anyone of eight data lines. Thus there are 16
possible combinations of lines and logic levels since there are two possible levels
on each line and only one line can be asserted during a parallel poll. The
PARALLEL POLL ENABLE command consists of an 8-bit byte whose bits are
arranged as follows (the decimal equivalent value of the byte falls in the range
of 96 through 111):
D7 D6 D5 D4 D3 D2 Dl DO Decimal Range
0
1
1 0
L X X X
96-111
where:
• The upper four bits are a fixed pattern of logical 0 (bits D7 and D4)
and logical 1 (bits D6 and D5) .
• Bit D3 (response logic level) determines whether data line D3 is to be
asserted (driven to its ground-true state) or released (allowed to float to
its high-false state) by the device when responding to a parallel poll if
service is needed. If bit D3 is set (1), the device responding to the poll
drives the data line low if service is needed. If D3 is not set (0), the
device responding to the poll drives the data line low if service is
not
needed (bit value
=
0). This bit is most commonly set to a value of
1.
3-36 Controlling the HP-IB Interface