HP 8921A, Руководство программиста

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Chapter 5, Advanced Operations
Passing Control
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.
Pass Control Examples
The following examples illustrate how pass control could be implemented in two
of the common Test Set operating configurations:
1. Test Set controlled by an external controller, and
2. Test Set running an IBASIC program with an external Controller connected to HP-IB
bus.
Passing Control While the Test Set is Controlled by an External Controller
This example illustrates passing control between the Test Set and an external
controller while the Test Set is being controlled by the external controller. In this
mode the Test Set is NOT configured as the System Controller. Generally
speaking, in this mode of operation the Test Set is considered just another device
on the HP-IB bus and its Controller capabilities are not used. However, it may be
desirable, under certain conditions, to print a Test Set screen to the HP-IB printer
for documentation or program debugging purposes. With manual intervention it is
possible to have the Active Controller pass control to the Test Set, have the
operator select and print the desired screen, and then pass control back to the
formerly Active Controller. The following steps outline a procedure for
accomplishing this task. The example is based upon having an HP 9000 Series
300 Workstation as the external controller connected to the Test Set through the
HP-IB bus. Further, it assumes that the HP-IB interface in the HP 9000 Controller
is set to the default select code of 7 and address of 21.