ATmega1284P datasheet(40/468 Pages) ATMEL

номер детали	ATmega1284P

подробное описание детали	8-bit Microcontroller with 16/32/64/128K Bytes In-Sytem Programmable Flash

PDF	468 Pages

Scroll/Zoom	100%

производитель	ATMEL [ATMEL Corporation]

домашняя страница	http://www.atmel.com

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8152G–AVR–11/09

ATmega164PA/324PA/644PA/1284P

neither the clock frequency corresponding to the previous setting, nor the clock frequency corre-

sponding to the new setting.

The ripple counter that implements the prescaler runs at the frequency of the undivided clock,

which may be faster than the CPU's clock frequency. Hence, it is not possible to determine the

state of the prescaler - even if it were readable, and the exact time it takes to switch from one

clock division to the other cannot be exactly predicted. From the time the CLKPS values are writ-

ten, it takes between T1 + T2 and T1 + 2 * T2 before the new clock frequency is active. In this

interval, 2 active clock edges are produced. Here, T1 is the previous clock period, and T2 is the

period corresponding to the new prescaler setting.

To avoid unintentional changes of clock frequency, a special write procedure must be followed

to change the CLKPS bits:

Write the Clock Prescaler Change Enable (CLKPCE) bit to one and all other bits in

CLKPR to zero.

Within four cycles, write the desired value to CLKPS while writing a zero to CLKPCE.

Interrupts must be disabled when changing prescaler setting to make sure the write procedure is

not interrupted.

ATmega1284P датащи(PDF) 40 Page - ATMEL Corporation