The Design Of Multi-Function Equal-Accuracy Digital Cymometer Based On CPLD

The reach paper mainly discusses the design process of multi-function cymometer that uses CPLD to count the frequency measurement and cymometer is also controled by signal chip computer. The cymometer makes use of equal-accuracy design that can overcome the disadvantage of traditional measuring principle, which precision declines as measured signal frequency does. The equal-accuracy measurement not only has higher measuring precision, but also can keep invariable measuring precision in whole area of frequency.This cymometer uses CPLD to realize the measuring count of frequency , period, pulse width and occupy-empty ratio. Signal chip computer completes the test control , data processing and display output of the system.This essay discusses the compose of hardware circuit and software control flow of signal chip computer in detail. Hardware circuit includes key control module , display module , plastic module of input signal , single chip computer control module and CPLD main control module.The cymometer adopts singal chip computer AT89C51 of Atmel company and EPM7128SLC84-15 of Altera company. Key control module has 5 function key and 3 time selection key. A chip 74LS165 completes the key value input. Display module uses eight 74LS165s to realize the serial display of LED. First, the measuring signal amplitude is limited. Second, the signal is amplified by two class direct coupling amplifier. Finally, the signal inputs CPLD after it is trimed by Smitter trigger. Standard frequency is 50MHz. Software program of singal chip computer is writed by assembly language. Some of software program is corresponded to every hardware part, the others includ data count and transform.