s3c72m9 Samsung Semiconductor, Inc., s3c72m9 Datasheet - Page 206

• Manufacturer Part Number: s3c72m9
• Description: The S3c72m5/s3c72m7/s3c72m9 Single-chip Cmos Microcontroller Has Been Designed For High Performance Using Samsung S
• Manufacturer: Samsung Semiconductor, Inc.

OSCILLATOR CIRCUITS
SYSTEM CLOCK MODE REGISTER (SCMOD)
The system clock mode register, SCMOD, is a 4-bit register that is used to select the CPU clock and to control
main and sub-system clock oscillation. RESET clears all SCMOD values to logic zero, selecting the main system
clock (fx) as the CPU clock and starting clock oscillation.
It's SCMOD.0, SCMOD.2, and SCMOD.3 bits can be manipulated by 1-bit write instructions. (In other words,
SCMOD.0, SCMOD.2, and SCMOD.3 cannot be modified simultaneously by a 4-bit write.) Bit 1 is always logic zero.
A subsystem clock (fxt) can be selected as the system clock by manipulating the SCMOD.3 and SCMOD.0 bit
settings. If SCMOD.3 = "0" and SCMOD.0 = "1", the subsystem clock is selected and main system clock
oscillation continues. If SCMOD.3 = "1" and SCMOD.0 = "0", fxt is selected, but main system clock oscillation
stops.
If you have selected fx as the CPU clock, setting SCMOD.3 to "1" will not stop main system clock oscillation. This
can only be done by a STOP instruction.
6-6
FB7H
NOTE:
SCMOD.3
SCMOD.3
You can use SCMOD.2 as follows (ex; after data bank was used, a few minutes have passed):
Main operation
external input)
SCMOD Register Bit Settings
0
0
1
SCMOD.2
Table 6-3. System Clock Mode Register (SCMOD) Organization
0
1
SCMOD.2
sub-operation
Table 6-4. SCMOD.2 for Sub-oscillation On/Off
sub-operation
SCMOD.0
0
1
1
"0"
main operation
sub-idle (LCD on, after a few minutes later without any
SCMOD.0
Disable sub system clock
Enable sub system clock
Sub-oscillation on/off
CPU Clock
S3C72M5/C72M7/C72M9/P72M9 (Preliminary Spec)
SCMOD.2 = 1
Resulting Clock Selection
fxt
fxt
fx
main stop mode (LCD off).
fx Oscillation
On
On
Off