In message , Ari Wahyudi writes >On Sun, 9 Aug 1998, Nigel Goodwin wrote: >> >I read about 50MHZ Freqmeter developed bySimone Benvenuti and Andrea >> >Geniola using PIC16C84. >> >I just don't understand how it works. HOw the PIC can measure such that >> >high frequency, since it only use 4MHz clock frequency.. >> >Anybody can explain? >> >> It uses the built-in prescaler, this is effectively a 16 bit hardware >> counter which can be clocked by the incoming frequency. The counter can >> be read (by devious means!) after a predetermined time interval, and the >> frequency calculated. > >But PIC16C84 datasheet/manual mention that external clock is >synchronized with Osc Clock, and it is necesary for TOCKI to high at >least 2Tosc and low for at least 2Tosc.. That's for input to TMR0, not the prescaler. Leon -- Leon Heller: leon@lfheller.demon.co.uk http://www.lfheller.demon.co.uk Amateur Radio Callsign G1HSM Tel: +44 (0) 118 947 1424 See http://www.lfheller.demon.co.uk/dds.htm for details of a simple AD9850 DDS system. See " "/diy_dsp.htm for a simple DIY DSP ADSP-2104 system.