Monitoring System Operation

Monitoring System Operation

Interrupt Process

The interrupt process begins when the analyzer \requests" attention by setting the HP-IB service-request (SRQ) line true. The computer responds by branching to a special subroutine that examines the status of each instrument on HP-IB. Computer operation then branches to another subroutine that

is determined by the status of the instrument that requested service (the analyzer in this case). In this way, the computer \services" the analyzer's \request." These steps are summarized below:

1.Computer monitors HP-IB service-request (SRQ) line.

2.Analyzer requests service by setting SRQ line true.

3.Computer branches to subroutine that examines analyzer state.

4.Computer branches to subroutine determined by analyzer state.

Several system-level commands are required to make the computer responsive to service requests. The HP BASIC command, ENABLE INTR (enable interrupt), tells the computer to monitor the service-request line. The on-interrupt command, ON INTR, speci￿es where the computer program will branch when a service request occurs. If more than one service request is possible, the serial-poll command, SPOLL, is needed to examine the nature of the service request. These HP BASIC commands, ENABLE INTR, ON INTR, and SPOLL, are used with the HP 9000 Series 200 and 300 computers.

Analyzer Status-ByteThe analyzer status-byte register is the communicating link between the

Registeranalyzer and the computer. The status-byte register indicates what state the analyzer is in.

The status-byte register consists of eight bits. Bits 0, 1, 2, 4, and 5 represent particular aspects of analyzer operation, such as end-of-sweep, or error conditions. These are listed in Table 1-13. The state of these bits, set (true) or cleared (false), is determined by the analyzer state.

If the service-request mode is enabled, all of the status-byte bits re￿ect the current state of the analyzer until the conditions of a service request are met.

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