National Instruments GPIB-SCSI-A, Руководство пользователя

Страница: 116 / 413

Chapter 5 S Mode Functions
© National Instruments Corp. 5-49 GPIB-SCSI-A User Manual
ln - Check for the Presence of a Listening Device
on the Bus
Type: Specialized Controller function.
Purpose: This command is used to determine whether or not there is a
listening device at the specified address.
Format:
Bit 7 6 5 4 3 2 1 0
Byte
0 Opcode = D2H
1 GPIB Primary Address Reserved
2 GPIB Secondary Addr. (Opt.) Mode Reserved
3 Reserved
4 Reserved
5 Reserved
Remarks: This command determines whether or not there is a listening
device at the GPIB address specified by the GPIB Primary
Address and the GPIB Secondary Address arguments. To
indicate that the GPIB Secondary Address contains a valid
device address, Mode must be set to 1.
This command returns one byte of data. If the device at the
specified address is listening, the byte has a non-zero value. If
there is no listening device at the specified address, a zero is
returned.
If Mode is 1, and the GPIB Secondary Address argument has
the value 31 (1F hex), the byte returned from the command
reflects whether a listening device is present on any of the
secondary addresses associated with the specified GPIB
Primary Address.
If this is the first function you call that requires GPIB
Controller capability, and you have not disabled System
Controller capability with
rsc
, the GPIB-SCSI-A sends