Introduction

The last several chapters of this book describe a detailed approach to data acquisition using the I/O ports presented in Chapter 3. The parallel data collector, as it's called, consists of the ports, the control/data interface (Chapter 7), the ADC module (Chapter 8) and an applications module. Any computer with suitable ports can operate the hardware and support the software.

Chapter 9 presented an example applications module which determines counts, times and voltages. A characteristic of the measurements is that software waits for data ready and then inputs and stores values. Because of the time required for these operations, the minimum counting interval, shortest measurable time, and maximum conversion rate depend on the computer's speed and the software's efficiency. Cases may arise which require smaller intervals, shorter times and/or higher rates. This chapter presents an applications module which automatically converts voltages and stores the values in its own memory. The system increases the maximum rate and works identically on original PC's, Apples II's and the latest computers. The approach also applies to counting and timing measurements.

The Fast Voltage Measurer (FVM) determines the voltage of one source at 8-bit accuracy with the rate and number of conversions programmable. The maximum 40K measurements/second arises from the AD573's 20μsec conversion time, and the maximum number of measurements equals 32K, the storage capacity of four 6264 8K IC's. Data acquisition starts when both Software Start/Stop (S-S/S*) and External Start (EX-S) become high. Software monitors for the end of data acquisition after which the stored values are read and processed as desired.