| Frequency measurement is one of the most fundamental and critically important measurements in electronic surveying area. The frequency signal has a strong anti-interference and easy to transport so that it can give a relative highly precision measurement. That's why people are paying more attention on studying ways of the frequency measurement.Equal-precision measurement eliminates the error plus-minus 1 of the tested signal technique, and catch the equal-precision measurement in the whole test channel. The accuracy of the measured signal will not vary with the frequency of measured signal. In researching design of equal-precision digital cymornetre of this paper, I introduced EDA technique which is prevalent in field of digital designs nowadays. Centering on CPLD, together with STC12LE1052 Single-Chip Microcomputer, and follow the multi-circle synchronization frequency measuring method, it realizes the equal-precision measurement of signal frequency from 1Hz to 1MHz. In order to accoplish variety of sequential logic controlling, tally function and indication, this design uses a EPM240T100 chip of series MAX II from ALTEAR company. It can use VHDL language programming to finish CPLD software design, programmng, debugging, simulation and download on the platform Quartus II afford by ALTEAR company. Use SCM EPM240T100 to accomplish the keyboard function and process to CPLD to control the display date.This system combines the controlling flexibilty of SCM and the on-the-spot programming of CPLD chip. It's not only shorten the cycle of researching and developing, but also make the system compact and small size, high reliable, has a broad range of frequency measurement and extremely accurate. This paper has particularly described the top-to—bottom design method of the system,the circuit composite of the hardware and the software program device of CPLD and the SCM. With a production of physical simulation and hardware verification, the measured precision and velocity have been obtained.
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