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Introduction to HS488
This appendix describes HS488 and the sequence of events in high-speed data transfers.
National Instruments has designed a high-speed data transfer protocol for IEEE 488 called
HS488. This protocol increases performance for GPIB reads and writes up to 8 Mbytes/s,
depending on your system.
If HS488 is enabled, the TNT4882C hardware implements high-speed transfers automatically
when communicating with HS488 instruments. If you attempt to enable HS488 on a GPIB
interface that does not have the TNT4882C hardware, the ECAP error code is returned.
Objectives
The following sections describe the objectives of HS488.
Faster Transfer Rates
HS488 enables transfer rates that are substantially faster than the IEEE 488 standard. 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 IEEE 488 Devices
HS488 is a superset of the IEEE 488 standard; thus, you can mix IEEE 488.1, IEEE 488.2, and
HS488 devices in the same system.
When connected to an HS488 device, the Controller does not need to be capable of HS488
noninterlocked transfers. While ATN is asserted, the Controller sources multiline messages to
HS488 devices just as it sources multiline messages to any IEEE 488 devices.
Automatic HS488 Detection
Addressed HS488 devices can detect whether other addressed devices are capable of HS488
transfers without the interaction of the Controller.
Compatibility with the IEEE 488.2 Standard
The HS488 protocol requires no changes to the IEEE 488.2 standard. Also, HS488 devices do
not need to be compliant with IEEE 488.2.
