MC68340 datasheet(105/441 Pages) FREESCALE

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MC68340 USER’S MANUAL

MOTOROLA

4.2.2.6.1 Periodic Timer Period Calculation. The period of the periodic timer can be

calculated using the following equation:

PITR count value

periodic interrupt timer period

EXTAL frequency/prescaler value

Solving the equation using a crystal frequency of 32.768-kHz with the prescaler disabled

gives:

PITR count value

periodic interrupt timer period

32768/1

periodic interrupt timer period

PITR count value

8192

This gives a range from 122

µs, with a PITR value of $01 (00000001 binary), to 31.128

ms, with a PITR value of $FF (11111111 binary).

Solving the equation with the prescaler enabled (PTP=1 in the PITR) gives the following

values:

PITR count value

periodic interrupt timer period

32768/512

periodic interrupt timer period

PITR count value

This gives a range from 62.5 ms, with a PITR value of $01, to 15.94 s, with a PITR value

of $FF.

For fast calculation of periodic timer period using a 32.768-kHz crystal, the following

equations can be used:

With prescaler disabled:

programmable interrupt timer period

PITR (122

µs)

With prescaler enabled:

programmable interrupt timer period

PITR (62.5 ms)

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

MC68340 Datasheet(PDF) 105 Page - Freescale Semiconductor, Inc