4509 Datasheet, PDF (58/142 Pages) Renesas Technology Corp – SINGLE-CHIP 4-BIT CMOS MICROCOMPUTER

4509 Group
(5) External clock
When the external signal clock is used for the main clock (f(XIN)),
connect the XIN pin to the clock source and leave XOUT pin open
(Figure 54). Do not execute the CRCK instruction in program.
Be careful that the maximum value of the oscillation frequency when
using the external clock differs from the value when using the ce-
ramic resonator (refer to the recommended operating condition).
Also, note that the RAM back-up mode (POF instruction) cannot be
used when using the external clock.
(6) Clock control register MR
Register MR controls the selection of operation mode and the opera-
tion source clock, and enable/stop of main clock. Set the contents of
this register through register A with the TMRA instruction. In addition,
the TAMR instruction can be used to transfer the contents of register
MR to register A.
(7) Clock control register RG
Register RG controls the on-chip oscillator. Set the contents of this
register through register A with the TRGA instruction.
4509
* Do not execute the CRCK
instruction in program.
XIN
XOUT VDD
VSS
External oscillation circuit
Fig. 54 External clock input circuit
Table 23 Clock control register MR
Clock control register MR
at reset : 11012
at RAM back-up : 11012
MR3
MR2
MR1
MR0
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 f(XIN) control bit (Notes 2, 5)
0
Main clock (f(XIN)) oscillation enabled
1
Main clock (f(XIN)) oscillation stop
0
Operation source clock selection bit (Notes 3, 5)
1
Main clock (f(XIN))
On-chip oscillator clock (f(RING))
R/W
TAMR/TMRA
RG0
Clock control register RG
On-chip oscillator (f(RING)) control bit
(Note 4)
at reset : 02
at RAM back-up : 02
0
On-chip oscillator (f(RING)) oscillation enabled
1
On-chip oscillator (f(RING)) oscillation stop
W
TRGA
Notes 1: “R” represents read enabled, and “W” represents write enabled.
2: Main clock cannot be stopped when the main clock is selected for the operation source clock.
3: The stopped clock cannot be selected for the operation source clock. In order to switch the operation source clock, generate the oscillation stabiliz-
ing wait time by software first and set the oscillation of the destination clock to be enabled.
4: On-chip oscillator cannot be stopped when the on-chip oscillator is selected for the operation source clock.
5: When changing the setting of MR1 and MR0 from “00” to “11”, make settings in the sequence “00” → “01” → “11”.
When changing the setting of MR1 and MR0 from “11” to “0”, make settings in the sequence “11” → “01” → “00”.
Rev.1.02 2006.12.22 page 58 of 140
REJ03B0147-0102