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Chapter 17 Clock Modulator
2.Clock Modulator Registers
● Clock modulator control register contents
Table 2-1 Function of each bit of the clock modulator control register (1 / 2)
Bit name Function
bit7 undefined
bit 6 to 5 Reserved Always write 0 to this bit.
bit 4 Reserved Always write 1 to this bit.
bit 3 FMOD RUN:
Modulator status
in frequency
modulation mode
bit
"0": MCU is running with unmodulated clock
"1": MCU is running with frequency modulated clock
• FMODRUN indicates the status of the modulator output clock in frequency
modulation mode (FMOD=1). If the output clock is frequency modulated,
MODRUN is set to 1, otherwise MODRUN is set to 0.
• After enabling the frequency modulation mode by setting FMOD to 1, the modulator
is calibrated. During this time, the clock is unmodulated. Therefore it takes several
us before the output clock switches to modulated clock and the FMODRUN bit is set
to 1. The calibration time depends on the frequency of the oscillator. At oscillator
(Fc) = 4MHz : Calibration time = 64.00us (calibration time = 256/Fc).
• During normal operation, after calibration is finished, the clock is not switched to
unmodulated clock anymore.
• Due to the synchronization of the FMOD signal and the synchronized switching to
unmodulated clock, it takes less than 9 x T0 (input clock period) before FMODRUN
changes to 0 and the clock switches to unmodulated clock after the modulator is
disabled.
• The FMODRUN bit is read only. Writing to FMODRUN has no effect.
• Before changing the parameter register CMPR, the modulator must be disabled ->
FMOD=0 and FMODRUN=0.
bit 2 Undefined