Introduction to HS488
Appendix C
GPIB-140 User Manual
C- 2
© National Instruments Corp.
No Added Cabling Restrictions beyond IEEE 488.1
Systems that meet the IEEE 488.1 requirements for higher speed operation meet the
HS488 requirements.
You should be aware of the limitations that affect HS488 usage:
•
Cabling requirements: Same as IEEE 488.1.
•
Does not reduce software overhead.
•
System throughput increases depend on data block size.
IEEE 488.1 Requirements for Higher Speed Operation
(T1 Delay
≥
350 ns)
The IEEE 488.1 standard specifies that devices intending high-speed operation must use
three-state, 48-mA drivers on most signals. Each device must add no more than 50-pF
capacitance on each signal, and all devices must be powered on.
The total cable length in a system must be no more than 15 m, or 1 m times the number
of devices in the system.
Additional HS488 System Requirements
An HS488 system must meet the IEEE 488.1 standard requirements described in the
preceding section, and HS488 devices must implement three new interface functions.
Talking devices must use the Source Handshake Extended (SHE) interface function,
which is an extension of the IEEE 488.1 SH function. Listening devices use the Acceptor
Handshake Extended (AHE) interface function, which is an extension of the IEEE 488.1
AHE function. Accepting devices must have at least a small buffer to store received data.
HS488 devices must implement the Configuration (CF) interface function. At system
power on, the Controller uses previously undefined multiline messages to configure
HS488 devices. The CF function enables devices to interpret these multiline messages.
Sequence of Events in Data Transfers
Figure C-1 shows a typical IEEE 488.1 data transfer and an HS488 data transfer. The
HS488 protocol modifies the 488.1 Source Handshake and Acceptor Handshake
functions. At the beginning of each data transfer, the HS488 source and acceptor
functions determine whether all active Talkers and Listeners are capable of HS488
transfers. If the addressed devices are HS488 capable, they use the HS488