Measurement Computing Extender 488HS Rev.2.0 - Manual (Page 18)

Section 2 Getting Started
2.10
8. Local extender receives parallel poll response on the link port and sends it to the local
IEEE 488 bus.
9. Controller reads parallel poll response.
Since most controllers read the parallel poll response shortly after asserting EOI and ATN
(within 2 µs), the use of a bus extender may not provide the parallel poll response back to the controller in
the allotted time. For applications that use the parallel poll command, the interconnecting cable length
should be such that time delays will not affect the parallel poll response. The following example may be
used to help determine the response time to a parallel poll in your system.
If a cable length of 10 m. is used, the parallel poll response time would be calculated as shown
below (from the previous parallel poll delay explanation):
Step Time Delay (approximate)
1 0
2 20 ns
3 59 ns (5.9 ns/meter) X (Interconnecting cable length)
4 20 ns
5 140 ns (device dependent)
6 20 ns
7 59 ns (5.9 ns/meter) X (Interconnecting cable length)
8 20 ns
Total 338 ns Total parallel poll response time
Since the IEEE 488 controller will wait 2 µs before reading the parallel poll response, the 338 ns
response time is well within the required 2 µs response time. For distances greater than 150 meters, the
parallel poll response may not be returned to the controller in the allotted time. The time is dependent on
the response time of the instruments on the remote bus.