Enabling HS488 Transfers
To enable HS488 for your GPIB interface, use the ibconfig function (option IbcHSCableLength). The value passed to ibconfig should specify the number of meters of cable in your NI-488.2 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 interface 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 traditional NI-488.2 calls, the NI-488.2 software automatically sends the HS488 configuration message to devices. If you set the HS488 cable length in Measurement & Automation Explorer to a non-zero value, 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 configuration message again, the next time you call a device-level function.
If you are using board-level traditional NI-488.2 calls or multi-device NI-488.2 calls 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 cable in your system. It is called the Configure (CFGn) message. Because HS488 can operate only with cable lengths of 1 to 15 meters, only CFGn values of 1 through 15 (hex 61 through 6F) are valid. If the cable length was configured properly in Measurement & Automation Explorer, you can determine how many meters of cable are in your system by calling ibask (option IbaHSCableLength) in your application. For CFE and CFGn messages, refer to the IEEE 488 Command Messages section.
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