National Instruments GPIB-PC - Manual (Page 111)

BASICA/QuickBASIC GPIB-PC Function Calls Section Four A
GPIB-PC User Manual 4A-36 ©National Instruments Corp.
BASICA/QuickBASIC BASICA/QuickBASIC
IBIST IBIST
Purpose: Set or clear individual status bit for Parallel Polls
Format: CALL IBIST (BD%,V%)
Remarks: BD% specifies an interface board. If V% is non-zero, the
individual status bit is set. If V% is zero, the bit is cleared.
The IBIST function is used when the GPIB-PC
participates in a parallel poll that is conducted by another
device that is the Active Controller. The Active Controller
conducts a parallel poll by asserting the EOI signal to send
the Identify (IDY) message. While this message is active,
each device which has been configured to participate in the
poll responds by asserting a predetermined GPIB data line
either true or false, depending on the value of its local ist
bit. The GPIB-PC, for example, can be assigned to drive
the DIO3 data line true if ist=1 and false if ist=0;
conversely, it can be assigned to drive DIO3 true if ist=0
and false if ist=1.
The relationship between the value of ist, the line that is
driven, and the sense at which the line is driven is
determined by the Parallel Poll Enable (PPE) message in
effect for each device. The GPIB-PC is capable of
receiving this message either locally, via the
IBPPC
function, or remotely, via a command from the Active
Controller. Once the PPE message is executed, the
IBIST
function changes the sense at which the line is driven
during the parallel poll, and in this fashion the GPIB-PC
can convey a one-bit, device dependent message to the
Controller.
When IBIST is called and an error does not occur, the
previous value of ist is stored in IBERR% .
Refer also to IBPPC and Table 2.1.