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a table pointed to by the value (address) in memory location k2. Increase k2.

The behavior of the processor consists of the familiar fetch-execute cycle. The processor normally waits until the computer sets the start-flag, before proceeding. The instruction-pointer is picked up from memory location k1. The instruction-pointer is then used to address various instructions. Each instruction is then fetched, decoded, and executed. The 4 instruction types have very simple actions, as defined in the flowcharts.

When a value is found to be out of range, the scan address and the out of range value are placed in a list which is addressed by memory location k2. This location is continuously updated. At the completion of the process, the Halt instruction sets the Done-flag which signals the computer that the Scan cycle has been carried out.


1. What is the maximum scanning rate, assuming all channels are within range, and all use the same range?

2. Modify the design to place the sampled value in the same 16-bit word as the channel number.


There are systems related to the EPUT meter described in Chapter 5 that are used in process control and communication. Event counting systems are often connected to a computer because other processing is carried out within the computer, including closed-loop control The purpose of an RTM system used as an adjunct to a computer would be to lighten the processing load associated with the basically trivial, but time consuming, operation of counting. As we indicated in the EPUT meter example of Chapter 5, a minicomputer dedicated to counting could only handle 1/3 the counting rate of the RTM system.

Two types of event input signals exist in process control. First, uni-directional inputs count in one direction (i.e., only increment) and are encoded as either events or as pulse widths. Flow meters for gasses and liquids are typical devices. Each pulse output from the flow meter indicates an incremental movement of the meter, hence an incremental quantity of material has flowed. By integrating the output of the meter (i.e., counting the pulse outputs from it) the flow is recorded.

The second similar, but bi-directional, counting system of this type is the incremental stepping motor which controls either a rotational or linear position of a mechanism. For example, a stepping motor is given a command to move either forward or reverse. The motor itself has no output that can be used to detect the position of the mechanism being moved. There is usually some other part of the system which provides this feedback as to the actual position of the mechanism. Often, however, no incremental or absolute feedback is used. The feedback as to the gross position for calibration is obtained from two limit reference switches indicating when the motor is in the extreme position.

Alternatively, there may be direct coupling of an input transducer to give the actual position (using an optical or magnetic position encoder, for example). This type of indicator has an output that indicates movement of +1 or -1 position, together with information about the absolute (limit) position.



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