s3c72m9 Samsung Semiconductor, Inc., s3c72m9 Datasheet - Page 201

• 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.

S3C72M5/C72M7/C72M9/P72M9 (Preliminary Spec)
OSCILLATOR CIRCUITS
6
OSCILLATOR CIRCUITS
OVERVIEW
The S3C72M5/C72M7/C72M9 microcontroller have two oscillator circuits: a main system clock circuit, and a
subsystem clock circuit. The CPU and peripheral hardware operate on the system clock frequency supplied through
these circuits. Specifically, a clock pulse is required by the following peripheral modules:
— LCD controller
— Basic timer
— Timer/counter 0 and 1 (1A/1B)
— Watch timer
— Serial I/O interface
— Clock output circuit
CPU Clock Notation
In this document, the following notation is used for descriptions of the CPU clock:
fx
Main-system clock
fxt Sub-system clock
fxx Selected system clock
Clock Control Registers
The power control register, PCON, is used to select normal CPU operating mode or one of two power-down modes
— stop or idle. Bits 3 and 2 of the PCON register can be manipulated by a STOP or IDLE instruction to engage stop
or idle power-down mode.
The system clock mode control register, SCMOD, lets you select the main system clock (fx) or a subsystem clock
(fxt) as the CPU clock and to start (or stop) main/sub system clock oscillation. The resulting clock source, either
main system clock or subsystem clock, is referred to as the selected system clock (fxx).
The main system clock is selected and oscillation started when all SCMOD bits are cleared to logic zero. By setting
SCMOD.3 and SCMOD.0 to different values, you can select a subsystem clock source and start or stop main/sub
system clock oscillation. Main system clock oscillation can be stopped by setting SCMOD.3 only when the
subsystem clock is operating. To stop main system clock oscillation (assuming the main system clock is selected),
you must use the STOP instruction instead of manipulating SCMOD.3.
The main system clock can be divided by 4, 8, or 64. By manipulating PCON bits 1 and 0, you select one of the
following frequencies as the selected system clock (fxx).
fx
fxt
fx
fx
,
,
,
4
4
8
64
When the SCMOD and PCON registers are both cleared to zero after RESET, the normal CPU operating mode is
enabled, a main system clock of fx/64 is selected, and main system clock oscillation is initiated.
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