Is there oscillation matching data with the crystal oscillator?
Answer : From a viewpoint of the oscillator characteristic, the crystal oscillator requires, in many cases, strict specifications.
So, we recommend to obtain oscillation matching data together with the board. For the ceramic oscillator, Murata Manufacturing
Co. and Matsushita Electronic Components Co. provide the obtained oscillation matching data.
How much is the recommended capacitance of the capacitor of the high-speed oscillation and low-speed oscillation?
Answer : Oscillation may tentatively occur with the capacitor of about 20 pF for the high-speed oscillation and 15 pF for the low-speed
oscillation. However, the recommended capacitances depend on the oscillator and board to be used. So, we recommend to obtain
matching data.
Is it necessary to connect a feedback resistor in the oscillation circuit?
Answer : Almost all oscillation circuits of FMC-16LX series are equipped with feedback resistors. So, you need not connect a feedback
resistor to the user board. Confirm this by referring to the oscillation pin circuit type in the hardware manual.
Answer : The damping resistor is used to form low-pass filter with the load capacitor and reduces the higher gain in order to suppress
abnormal oscillation of high frequencies. Moreover, the IC gain is limited to provide better matching between the IC and resonator.
So, unnecessary ringing decreases, thus enabling suppression of overshoot and undershoot. For details, contact a manufacturer
of the oscillator used.
Teach me the connection method when inputting an external clock as a clock source.
Answer : When a frequency is low, there is no problem when clocks are input to X0 and X1 is open. However, when the frequency is high,
you need to input clocks to X0 and clocks with their reversed phase to X1.
How large is the flexibility of the oscillation circuit designed?
Answer : Oscillator manufacturers usually guarantee the matching characteristic with the oscillation flexibility of 10 dB or more.
So, the oscillation circuit of up to 10 dB or more is mounted with frequencies in the microcomputer operation guarantee range.
Why does the negative resistance of the oscillation circuit increases when the resonator frequency is made lower?
Answer : The negative resistance of the oscillation circuit depends on the characteristic of the oscillation cell. When the negative
resistance is used under the same circuit condition, it decreases with the higher frequency. This is because the negative
resistance becomes smaller when the oscillation cell has the smaller gain at higher frequency.
Why does a microcomputer run at low speeds when microcomputer clock is removed midway or stopped forcibly and externally?
Answer : The possible reason is that, since the PLL is continuing to run even if PLL mounted on the microcomputer stops supplying oscillation,
the CPU is operating at low speeds. From an oscillation mechanism viewpoint, at normal operation (when the oscillator is connected),
PLL cycles are adjusted by using the cycle of the external oscillator as the reference at setting of internal PLL and the
CPU operates at an adjusted PLL frequency. So, when a clock is stopped in that status, the built-in PLL attempts to adjust
itself to the stopped clock, thus causing the PLL to gradually slow down and continues to run. This low-speed operation cannot
be ensured because it varies depending on products.
Oscillation stabilization wait time = 2 raise to 18 power/oscillation clock frequency. In this equality, does "oscillation
clock frequency" mean an external input clock or machine cycle?
Answer : The oscillation clock frequency is a frequency of an external oscillator. So, if external 16 MHz is connected, 16 ms clock
is the oscillation stabilization wait time.
