4518 Datasheet, PDF (68/160 Pages) Renesas Technology Corp – SINGLE-CHIP 4-BIT CMOS MICROCOMPUTER

4518 Group
(1) Main clock generating circuit (f(XIN))
The ceramic resonator, RC oscillation or quartz-crystal oscillator
can be used for the main clock of this MCU.
After system is released from reset, the MCU starts operation by
the clock output from the on-chip oscillator which is the internal os-
cillator.
When the ceramic resonator is used, execute the CMCK instruc-
tion. When the RC oscillation is used, execute the CRCK
instruction. When the quartz-crystal oscillator is used, execute the
CYCK instruction. The oscillation start/stop of main clock f(XIN) is
controlled by bit 1 of register MR. The system clock is selected by
bit 0 of register MR. The oscillation circuit by the CMCK, CRCK or
CYCK instruction can be selected only at once. The oscillation cir-
cuit corresponding to the first executed one of these instructions is
valid.
Execute the CMCK, CRCK or CYCK instruction in the initial setting
routine of program (executing it in address 0 in page 0 is recom-
mended). Also, when the CMCK, CRCK or CYCK instruction is not
executed in program, this MCU operates by the on-chip oscillator.
Reset
On-chip oscillator operation
CMCK instruction
CRCKinstruction
CYCK instruction
• Main clock: ceramic resonance
• On-chip oscillator: operating
• System clock: on-chip oscillator clock
• Main clock: RC oscillation circuit
• On-chip oscillator: operating
• System clock: on-chip oscillator clock
• Main clock: Quartz-crystal circuit
• On-chip oscillator: operating
• System clock: on-chip oscillator clock
• Set the main clock (f(XIN)) oscillation by bit 1 of register MR.
• Switch the system clock by bit 0 of register MR.
Also, when system clock is switched after main clock oscillation is started,
generate the oscillation stabilizing wait time by program if necessary.
• Set the on-chip oscillator clock oscillation by register RG.
Fig. 57 Switch to ceramic resonance/RC oscillation/quartz-crystal oscillation
Rev.3.01 2005.06.15 page 68 of 157
REJ03B0008-0301