255_FREQUENCY_SYNTHESIZER

Published:2009/7/6 2:21:00 Author:May | From:SeekIC

Circuit as shown for programmable counter section of Exar XR-2240 programmable timer/counter provides square-wave outputs at 255 discrete frequencies from given internal time-base setting.Output is positive pulse train with pulse width T determined by values of R and C. Period is equal to (N + 1)T where N is programmed count in counter of IC. Counter output connections to output bus determine value of N; if pins 1,3,and 4 are connected to bus, N is 1 + 4 + 8 or 13 and period is 14T, Supply voltage range is 4-.15 V.If counter cannot be triggered when using supplyabove 7V and less than 0.1μF forC, connect 300 pF from pin 14 to ground.- Timer Data Book, Exar Integrated Systems, Sunnyvale, CA, 1978, p 11-18.



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