4524_M Datasheet, PDF (254/310 Pages) Renesas Technology Corp – 4-BIT CISC SINGLE-CHIP MICROCOMPUTER 720 FAMILY / 4500 SERIES

4524 Group
APPLICATION
2.10 Oscillation circuit
2.10.3 Related register
(1) Clock control register MR
Table 2.10.1 shows the clock control register MR.
Set the contents of this register through register A with the TMRA instruction.
The contents of register MR is transferred to register A with the TAMR instruction.
Table 2.10.1 Clock control register MR
Clock control register MR
at reset : 11002 at power down : state retained
MR3
MR2
MR1
MR3 MR2
Operation mode
0 0 Through-mode (frequency not divided)
Operation mode selection bits 0 1 Frequency divided by 2 mode
1 0 Frequency divided by 4 mode
1 1 Frequency divided by 8 mode
Main clock oscillation circuit _{0 Main clock oscillation enabled}
control bit
1 Main clock oscillation stop
MR0 ^{System clock selection bit}
0 Main clock (f(XIN) or f(RING))
1 Sub-clock (f(XCIN))
Note: “R” represents read enabled, and “W” represents write enabled.
R/W
2.10.4 Notes on use
(1) Clock control
Execute the CMCK or the CRCK instruction to select the main clock (f(XIN)) in the initial setting
routine of program (executing it in address 0 in page 0 is recommended).
The oscillation circuit by the CMCK or CRCK instruction can be selected only at once. The oscillation
circuit corresponding to the first executed one of these two instructions is valid. Another oscillation
circuits and the on-chip oscillator stop.
(2) On-chip oscillator
The clock frequency of the on-chip oscillator depends on the supply voltage and the operation
temperature range.
Be careful that margin of frequencies when designing application products.
Also, the oscillation stabilize wait time after system is released from reset is generated by the on-
chip oscillator clock. When considering the oscillation stabilize wait time after system is released
from reset, be careful that the margin of frequencies of the on-chip oscillator clock.
(3) External clock
When the external clock signal is used as the main clock (f(XIN)), note that the power down mode
(POF or POF2 instruction) cannot be used.
(4) Value of a part connected to an oscillator
Values of a capacitor and a resistor of the oscillation circuit depend on the connected oscillator and
the board. Accordingly, consult the oscillator manufacturer for values of each part connected the
oscillator.
Rev.2.00 Aug, 06 2004
REJ09B0107-0200Z
2-90