Precautions For Frequency Synthesizer - Renesas M16C Series User Manual

M30245 Group

2.7.3 Precautions for Frequency synthesizer

(1) Bits 6 and 5 of frequency synthesizer control register are set to (bit6, bit5)=(1, 1) at reset. When using
the frequency synthesizer, we recommended to set to (bit6, bit5)=(1, 0).
(2) Set f
SYN
(3) The value of f
(4) When the frequency synthesizer is enabled, do not use the output of the frequency synthesizer until
after a 2~5ms delay. That will stabilize the output. Also, after the frequency synthesizer has been
enabled, because the output is temporarily (2-5ms) unstable, the contents of none of the registers
should be changed.
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(5) When using the frequency synthesizer, connect a low pass filter to the LPF terminal.
(6) The following setup for the frequency synthesizer should be done after hardware resest.
1. Cancel the protect register.
2. Set the frequency synthesizer related registers to generate the 48MHz clock that is necessary for
the f
3. Enable the frequency synthesizer by setting frequency synthesizer control register.
4. The protect register should be set to write disabled. A 3ms wait is necessary.
5. The frequency synthesizer locked status bit should be checked. It is necessary to recheck after a
wait of 0.1ms if it is "0" (unlocked).
6. Enable USB clock.
7. After waiting four cycles of the f or greater, the USB enable bit should be set to "1".
A minimum delay of 250ns is needed before performing any other USB related registers read/write
operations.
Rev.2.00 Oct 16, 2006
REJ09B0340-0200
to 12 MHz or lower.
should not be set below 1 MHz.
PIN
.
USB
page 126 of 354
2. Frequency synthesizer (PLL)