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Passing Control to the Test Set
Control is passed to the Test Set when it is addressed to TALK and then receives
the Take Control Talker (TCT) command. The programming or controller
command which implements the pass control protocol as outlined in the IEEE
488.1 and 488.2 Standards is language/controller specific. Refer to the appropriate
language/controller documentation for specific implementations.
Before passing control to the Test Set the Active Controller should send the Test
Set the address to use when passing control back. This is accomplished using the
*PCB Common Command. The *PCB command tells the Test Set which address
should be used when passing control back to another bus controller. Before
passing bus control to the Test Set, the currently active controller can use the
*PCB command to tell the Test Set where to send the Take Control (TCT)
command when the Test Set is ready to give up active control of the bus. The
command is followed by a number which contains the bus address of the device
that should become the next active controller. The number must round to an
integer in the range 0 to 30 decimal. The command may be followed by two
numbers. The first will be used as the primary address, the second as the
secondary address of the next active controller.
Requesting Control using IBASIC
The Test Set has the capability to request control of the bus from the Active
Controller from a running IBASIC program using the IBASIC command
EXECUTE ("REQUEST_CONTROL"). When the EXECUTE
("REQUEST_CONTROL") command is executed from a running IBASIC
program, the Request Control bit, bit 1, of the Test Set's Standard Event Status
Register is set to the TRUE, logic 1, condition. The Active Controller detects the
request in the Test Set's Standard Event Status Register either as a result of an
SRQ indication by the Test Set or by some polling routine which periodically
checks bit 1 of the Standard Event Status Register of all potential controllers on
the bus. The Active Controller would then send the Test Set the address to which
the Test Set is to later pass control using the *PCB Common Command. The
Active Controller would then pass control to the Test Set.
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Chapter 3, Operating Overview
Passing Instrument Control
91
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