Measurement Computing Isolator488 - Manual (Page 20)

Section 2 Getting Started
2.11
2.6.2 Cabling Length
The IEEE 488 specification allows for cabling distance between bus
devices of 2 meters (approx. 7 feet). The total worst case distance from the
two furthest devices is not allowed to exceed 20 meters (approx. 70 feet).
The addition of the Isolator488 does not increase this distance.
2.6.3 Signal Line Direction
The signal lines and their direction include....
Data Lines:
DIO1 - DIO7 Bidirectional
Handshake Lines:
DAV Bidirectional
NRFD Bidirectional
NDAC Bidirectional
Command Lines:
SRQ To Controller Bus
ATN To Instrument Bus
EOI Bidirectional
REN To Instrument Bus
IFC To Instrument Bus
The majority of the command lines have their signal direction fixed.
This forces bus control from the CONTROLLER bus.
When Attention (ATN) is asserted, the data lines, talker handshake
line (DAV) and the EOI line direction is forced from the CONTROLLER
to the INSTRUMENT port. The listener handshake lines (NRFD and
NDAC) are forced from the INSTRUMENT to the CONTROLLER port.
The commands are sent through the Isolator488 to the INSTRUMENT
port.