microprocessor based frequency counter

Posted on Feb 7, 2014

In order to make the circuit work, it is important to set the fuse bits inside the AVR micro controller correctly. Theses fuse bits can be set with the programmer that is used to flash the software. For those that are interested to understand the background, have a look at the ATmega16 datasheet pages 254-256. The logic of the bits is active low,

microprocessor based frequency counter
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i. e. programmed=0, unprogrammed=1. The bits that determine the clock source of the AVR, CKSEL 0. 3, come programmed when the chip is shipped, i. e. set to 0. That is the reason why the controller runs on internal clocking, and does not even start the crystal. By setting all CKSEL 0. 3 to unprogrammed (1), the external crystal is selected. The CKOPT programmed (0) switches the crystal from weak amplitude to full amplitude, so that the 74HC4040 gets enough input signal.

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