M38203M4 Datasheet, PDF (280/344 Pages) Mitsubishi Electric Semiconductor – 8-BIT SINGLE-CHIP MICROCOMPUTER

APPLICATION
2.11 Oscillation circuit
2.11.3 Oscillating operation
The start and stop sources for oscillating operation are described below.
(1) Oscillating operation
At reset release, the middle-speed mode is provided. At this time, only the main clock oscillates and
the XCIN and XCOUT pins function as I/O ports.
To use the sub-clock, set the P70, P71 pull-up (bit 4) of the PULL register A (address 001616) to “0”
and disconnect each pull-up resistor of the XCIN and XCOUT pins.
sMiddle-speed mode
The internal clock φ after reset release is obtained by dividing f(XIN) by 8 (f(XIN) is the frequency which
is input to the XIN pin).
When changing to the high-speed mode:
Set the main clock division ratio selection bit (bit 6) of the CPU mode register (address 003B16) to “0.”
When changing to the low-speed mode:
Change the mode according to the following procedure.
Œ Set the port Xc switch bit (bit 4) of the CPU mode register to “1.”
 Generate the oscillation stabilizing time of XCIN input by software.
Ž Set the internal system clock selection bit (bit 7) of the CPU mode register to “1.”
sHigh-speed mode
The clock obtained by dividing f(XIN) by 2 is an internal clock φ.
When changing to the middle-speed mode:
Set the main clock division ratio selection bit (bit 6) of the CPU mode register to “1.”
When changing to the low-speed mode:
Change the mode according to the following procedure.
Œ Set the port Xc switch bit (bit 4) of the CPU mode register to “1.”
 Generate the oscillation stabilizing time of XCIN input by software.
Ž Set the internal system clock selection bit (bit 7) of the CPU mode register to “1.”
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3820 GROUP USER’S MANUAL