Example - HP 9000 Series 300 Tutorials Manual

Using the previous example for calculating the mask value, device A is
configured to respond on line DO with a 1 when it wants service, but device B
requests service by placing a 0 on line D4. The binary value for sense is:
D7
D6
D5 D4 D3 D2 Dl
o
o
o
1
o
o o
The decimal equivalent of this number is 16; the correct value for sense.
If all devices on the bus respond to parallel polls with a 1 to request service,
the value for sense can always be 0, regardless of which parallel poll lines are
being monitored. If, on the other hand, all of devices request service with a 0,
the sense value can always be 255 (11111111 in binary). You need calculate
a special value for sense only if various devices on the bus respond with
dissimilar logic senses.
Example
Assume that you want to use hpib_wait_on_ppoll to wait for one of the four
devices on a bus to request service where the bus is configured as follows:
Parallel Poll Requests Service
Device Bus Address Response Line with a:
A
5
DO 1
B
7 Dl
0
C 9 D2 0
D 11 D3 1
Begin by calculating the mask value for hpib_wai t_on_ppoll. Since responses
can be expected on lines DO, Dl, D2, and D3, the correct mask value is:
Binary: Decimal:
o
0 0 0 1 1 1 1 15
3-44 Controlling the HP-IB Interface