s3c72m9 Samsung Semiconductor, Inc., s3c72m9 Datasheet - Page 204

• 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
POWER CONTROL REGISTER (PCON)
The power control register, PCON, is a 4-bit register that is used to select the CPU clock frequency and to control
CPU operating and power-down modes. PCON can be addressed directly by 4-bit write instructions or indirectly by
the instructions IDLE and STOP.
PCON bits 3 and 2 are addressed by the STOP and IDLE instructions, respectively, to engage the idle and stop
power-down modes. Idle and stop modes can be initiated by these instruction despite the current value of the enable
memory bank flag (EMB). PCON bits 1 and 0 are used to select a specific system clock frequency. There are two
basic choices:
— Main system clock (fx) or subsystem clock (fxt);
— Divided fx/4, 8, 64 or fxt/4 clock frequency.
PCON.1 and PCON.0 settings are also connected with the system clock mode control register, SCMOD. If
SCMOD.0 = "0" the main system clock is always selected by the PCON.1 and PCON.0 setting; if SCMOD.0 =
"1" the subsystem clock is selected.
RESET sets PCON register values (and SCMOD) to logic zero: SCMOD.3 and SCMOD.0 select the main system
clock (fx) and start clock oscillation; PCON.1 and PCON.0 divide the selected fx frequency by 64, and PCON.3 and
PCON.2 enable normal CPU operating mode.
+
To set the CPU clock to 0.95 µs at 4.19 MHz:
6-4
FB3H
PROGRAMMING TIP — Setting the CPU Clock
BITS
SMB
LD
LD
PCON.3
PCON.3
PCON.1
PCON Bit Settings
PCON Bit Settings
0
0
1
0
1
1
EMB
15
A,#3H
PCON,A
Table 6-1. Power Control Register (PCON) Organization
PCON.2
PCON.2
PCON.0
0
1
0
0
0
1
PCON.1
Normal CPU operating mode
Idle power-down mode
Stop power-down mode
If SCMOD.0 = "0"
Resulting CPU Clock Frequency
Resulting CPU Operating Mode
fx/64
fx/8
fx/4
PCON.0
S3C72M5/C72M7/C72M9/P72M9 (Preliminary Spec)
If SCMOD.0 = "1"
fxt/4