Chapter 5 Clock Generator; Ring Oscillator; Autocalibration Function; Ring Oscillator States - NEC V850ES/DJ2 User Manual

5.1 Ring Oscillator

To support a high frequency clock source for the MTRC an internal high speed Ring Oscillator is imple-
mented in the MTRC. This Ring Oscillator is controlled with SFRs to realize stop, restart and calibra-
tion.
After the release of the MTRESET pin the Ring Oscillator is stopped. It will be automatically started if
the MTCS signal will be set from "0" to "1".
Remark: For mass production tests the MTRC can be clocked alternatively direct from the FG2
device via the CLKOUT pin. This pin is internally connected with the CLK pin of the MTRC.
Due to EME reason this mode is not useful for real applications.

5.1.1 Autocalibration function

At the first start of the ring oscillator it is uncalibrated and therefore significant deviations from its basic
frequency (8 MHz) could be possible.
The Ring Oscillator Unit supplies an autocalibration function. With 5 specified calibration pulses at the
CS pin of the MTRC (therefore PCM0/WAIT pin at the FG2) direct after MTRES release, the Ring Oscil-
lator self-calibration unit adjusts the frequency iteratively.
The calculated calibration factor is stored in the MRCAL register. This register controls the calibration
unit of the Ring Oscillator to set its frequency to 8 MHz.

5.1.2 Ring Oscillator states

With the Ring Oscillator 3 different states have to be separated:
• Calibration Mode
• Start-up after MTRESET
• Start-up after Standby Mode release
At each state different actions are necessary to handle the Ring Oscillator. The basic separation
depends on the handling of the MRCAL register.

Chapter 5 Clock Generator

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