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Application Examples
Example 8: Parallel Polls
This example illustrates how you can use NI-488.2 routines to obtain information
from several IEEE 488.2 compliant devices at once by using a procedure called
parallel polling.
The process of manufacturing a particular alloy involves bringing three different
metals to specific temperatures before mixing them to form the alloy. Three vats
are used, each containing a different metal. Each is monitored by a GPIB ore
monitoring unit. The monitoring unit consists of a GPIB temperature transducer
and a GPIB power supply. The temperature transducer is used to probe the
temperature of each metal. The power supply is used to start a motor to pour the
metal into the mold when it reaches a predefined temperature. The three
monitoring units are connected to the IEEE 488.2 interface board of a computer
fitted with the NI-488.2M software and operated by an application using NI-
488.2 routines. The application obtains information from the multiple units by
conducting a parallel poll, then determines when to pour the metals into the
mixture tank. The following steps correspond to the program flowchart in Figure
2-8.
1.
The application initializes the GPIB by bringing the interface board in the
computer online.
2.
The application configures the temperature transducer in the first monitoring
unit by choosing which of the eight GPIB data lines the transducer uses to
respond when a parallel poll is conducted. The application also sets the
temperature threshold. The transducer manufacturer has defined the
individual status (ist) bit to be true when the temperature threshold is
reached, and the configured status mode of the transducer is assert the data
line. When a parallel poll is conducted, the transducer asserts its data line if
the temperature has exceeded the threshold.
3.
The application configures the temperature transducer in the second
monitoring unit for parallel polls.
4.
The application configures the temperature transducer in the third monitoring
unit for parallel polls.
5.
The application conducts non-GPIB activity while the metals are heated.
NI-488.2M SRM for OS/2
2-18
© National Instruments Corp.
Chapter 2
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