Samsung S3C2440A - Manual (Page 219)

CLOCK & POWER MANAGEMENT S3C2440A RISC MICROPROCESSOR
7 -12
NORMAL Mode
In Normal mode, all peripherals and the basic blocks including power management block, the CPU core, the bus
controller, the memory controller, the interrupt controller, DMA, and the external master may operate completely.
But, the clock to each peripheral, except the basic blocks, can be stopped selectively by software to reduce the
power consumption.
IDLE Mode
In IDLE mode, the clock to the CPU core is stopped except the bus controller, the memory controller, the interrupt
controller, and the power management block. To exit the IDLE mode, EINT[23:0], or RTC alarm interrupt, or the
other interrupts should be activated. (EINT is not available until GPIO block is turned on).
SLOW Mode (Non-PLL Mode)
Power consumption can be reduced in the SLOW mode by applying a slow clock and excluding the power
consumption from the PLL. The FCLK is the frequency of divide_by_n of the input clock (XTIpll or EXTCLK)
without PLL. The divider ratio is determined by SLOW_VAL in the CLKSLOW control register and CLKDIVN
control register.
Table 7-3. CLKSLOW and CLKDIVN Register Settings for SLOW Clock example
SLOW_VAL FCLK HCLK PCLK UCLK
1/1 Option
(HDIVN=0)
1/2 Option
(HDIVN=1)
1/1 Option
(PDIVN=0)
1/2 Option
(PDIVN=1)
0 0 0 EXTCLK or
XTIpll / 1
EXTCLK or
XTIpll / 1
EXTCLK or
XTIpll / 2
HCLK HCLK / 2 48 MHz
0 0 1 EXTCLK or
XTIpll / 2
EXTCLK or
XTIpll / 2
EXTCLK or
XTIpll / 4
HCLK HCLK / 2 48 MHz
0 1 0 EXTCLK or
XTIpll / 4
EXTCLK or
XTIpll / 4
EXTCLK or
XTIpll / 8
HCLK HCLK / 2 48 MHz
0 1 1 EXTCLK or
XTIpll / 6
EXTCLK or
XTIpll / 6
EXTCLK or
XTIpll / 12
HCLK HCLK / 2 48 MHz
1 0 0 EXTCLK or
XTIpll / 8
EXTCLK or
XTIpll / 8
EXTCLK or
XTIpll / 16
HCLK HCLK / 2 48 MHz
1 0 1 EXTCLK or
XTIpll / 10
EXTCLK or
XTIpll / 10
EXTCLK or
XTIpll / 20
HCLK HCLK / 2 48 MHz
1 1 0 EXTCLK or
XTIpll / 12
EXTCLK or
XTIpll / 12
EXTCLK or
XTIpll / 24
HCLK HCLK / 2 48 MHz
1 1 1 EXTCLK or
XTIpll / 14
EXTCLK or
XTIpll / 14
EXTCLK or
XTIpll / 28
HCLK HCLK / 2 48 MHz
In SLOW mode, PLL will be turned off to reduce the PLL power consumption. When the PLL is turned off in the
SLOW mode and the user changes power mode from SLOW mode to NORMAL mode, then the PLL needs clock
stabilization time (PLL lock time). This PLL stabilization time is automatically inserted by the internal logic with lock
time count register. The PLL stability time will take 300us after the PLL is turned on. During PLL lock time, the
FCLK becomes SLOW clock.