Measurement Computing Extender 488HS Rev.2.0 - Manual (Page 17)

Section 2 Getting Started
2.9
Length (Meters)
10 100 1000
10
100
1000
Extender488/HS Data Rate vs Cable Length
Since the IEEE 488 handshake is maintained across the entire link from the Local bus to the
Remote bus, it is highly unlikely that data will be lost. The only IEEE 488 transaction that could be
affected by long cable lengths is parallel poll (PPOL). If your application uses
parallel polling, you should
be aware of the time delays that are introduced into your system when any type of bus extender (including
the Extender488/HS) is installed.
In a system that does not use a bus extender, the following events occur when the controller
conducts a parallel poll:
1. Controller conducts parallel poll (asserts EOI and ATN).
2. Devices detect parallel poll state and respond by asserting a data line.
3. Controller reads parallel poll response from data bus.
In a system that uses bus extenders, the following delays are present when the controller conducts
a parallel poll:
1. Controller conducts parallel poll (asserts EOI and ATN)
2. Local extender detects parallel poll state and sends the message to the link port.
3. Message travels through the link cable and arrives at the remote extender after an amount
of time that depends on the length of the interconnecting cable.
4. Remote unit receives parallel poll state and sends it to the remote IEEE 488 bus.
5. Devices on the remote bus detect the parallel poll state and respond by asserting a data
line.
6. Response travels through remote extender to its link port.
7. Response travels through the link cable and arrives at the local extender after an amount
of time that depends on the length of the interconnecting cable.