National Instruments NI-488.2 High-Speed Data Transfers (HS488)

GPIB Programming Techniques Chapter 7

NI-488.2 User Manual for Windows 7-2 © National Instruments Corp.

You can use the ibconfig function to configure the software to inform you whether or

not the GPIB EOI line was asserted when the EOS byte was read. Use the

IbcEndBitIsNormal option to configure the software to report only the END bit in

ibsta when the GPIB EOI line is asserted. By default, the NI-488.2 driver reports END

in ibsta when either the EOS byte is read in or the EOI line is asserted during a read.

High-Speed Data Transfers (HS488)

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.

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. If HS488 is enabled, the

TNT4882C hardware implements high-speed transfers automatically when

communicating with HS488 instruments. To determine whether your GPIB interface

board has the TNT4882C hardware, use the GPIBInfo utility. If you attempt to enable

HS488 on a GPIB board that does not have the TNT4882C chip, the error ECAP is

returned.

To enable HS488 for your GPIB board, use the ibconfig function (option

IbcHSCableLength). The value passed to ibconfig should specify the number of

meters of cable in your GPIB configuration. If you specify a cable length that is much

smaller than what you actually use, the transferred data could become corrupted. If you

specify a cable length longer than what you actually use, the data is transferred

successfully, but more slowly than if you specified the correct cable length.

In addition to using ibconfig to configure your GPIB board for HS488, the Controller-

In-Charge must send out GPIB command bytes (interface messages) to configure other

devices for HS488 transfers.

If you are using device-level calls, the NI-488.2 software automatically sends the HS488

configuration message to devices. If you enabled the HS488 protocol in wibconf, the

NI-488.2 software sends out the HS488 configuration message when you use ibdev to

bring a device online. If you call ibconfig to change the GPIB cable length, the

NI-488.2 software sends out the HS488 message again the next time you call a device-

level function.

If you are using board-level functions or NI-488.2 routines and you want to configure

devices for high-speed, you must send the HS488 configuration messages using ibcmd

or SendCmds . The HS488 configuration message is made up of two GPIB command

bytes. The first byte, the Configure Enable (CFE) message (hex 1F), places all HS488

devices into their configuration mode. Non-HS488 devices should ignore this message.

The second byte is a GPIB secondary command that indicates the number of meters of