S3P72P9 datasheet(97/225 Pages) SAMSUNG

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OSCILLATOR CIRCUITS

S3C72P9/P72P9 (Preliminary Spec)

6-4

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.

FB3H

PCON.3

PCON.2

PCON.1

PCON.0

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.

Table 6-1. Power Control Register (PCON) Organization

PCON Bit Settings

Resulting CPU Operating Mode

PCON.3

PCON.2

Normal CPU operating mode

Idle power-down mode

Stop power-down mode

PCON Bit Settings

Resulting CPU Clock Frequency

PCON.1

PCON.0

If SCMOD.0 = "0"

If SCMOD.0 = "1"

fx/64

fxt/4

fx/8

fx/4

+ PROGRAMMING TIP — Setting the CPU Clock

To set the CPU clock to 0.95 µs at 4.19 MHz:

BITS

EMB

SMB

A,#3H

PCON,A

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