© National Instruments Corp.
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GPIB-140 User Manual
Appendix C
Introduction to HS488
This appendix describes HS488 and the sequence of events in high-speed data transfers.
HS488 is a proposed addition to the ANSI/IEEE Standard 488.1-1987. HS488 specifies
using a noninterlocked handshake protocol to transfer data between two or more devices.
By using the HS488 protocol, devices can transfer data at rates that are higher than the
rates that are possible by using the IEEE 488.1 protocol.
Objectives of HS488
Fast Transfer Rates
HS488 enables transfer rates that are substantially faster than the IEEE 488.1 standard
transfer rates. In small systems, the raw transfer rate can be up to 8 Mbytes/s. The faster
raw transfer rates improve system throughput in systems where devices send long blocks
of data. The physical limitations of the cabling system, however, limit the transfer rate.
Compatibility with Existing IEEE 488.1 Devices
HS488 devices are compatible with 488.1 devices. IEEE 488.1 devices and HS488
devices can exist in the same system, and they communicate with each other using 488.1
protocols.
A Controller does not need to be capable of HS488 noninterlocked transfers when
connected to an HS488 device. While ATN is asserted, a Controller sources multiline
messages to HS488 devices just as it sources multiline messages to any 488.1 devices.
No Additional Software Overhead—Automatic HS488 Detection
Addressed HS488 devices detect whether other addressed devices are also HS488
capable without the interaction of the Controller.
No Changes to the IEEE 488.2 Standard
The HS488 protocol requires no changes to the IEEE 488.2 standard. HS488 devices do
not need to be 488.2 compliant.
