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2.9.1.7 - Frequency Output (Mode 7) [U6 Datasheet]

Outputs a square wave at a frequency determined by the following formula:

frequency = TimerClockBase/(TimerClockDivisor*2*Timer#Value)

The Value passed should be between 0-255, where 0 is a divisor of 256. By changing the clock configuration and timer value, a wide range of frequencies can be output, as shown in the following table:

Table 2.9.1.7-1. Mode 7 Frequency Ranges

TimerClockBase

 

Divisor=1

Value =1

Divisor=1

Value = 256

0

4 MHz

2000000

7812.5

1

12 MHz

6000000

23437.5

2

48 MHz (Default)

24000000

93750

3

1 MHz /Divisor

500000

7.629

4

4 MHz /Divisor

2000000

30.518

5

12 MHz /Divisor

6000000

91.553

6

48 MHz /Divisor

24000000

366.211

The frequency output has a -3 dB frequency of about 10 MHz on the FIO lines. Accordingly, at high frequencies the output waveform will get less square and the amplitude will decrease.

The output does not necessarily start instantly, but rather has to wait for the internal clock to roll. For the Frequency Output mode, the start delay varies from 0.0 to TimerClockDivisor*256/TimerClockBase. For example, if TimerClockBase = 48 MHz and TimerClockDivisor = 256, the start delay will vary from 0 to 1.4 ms.

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