RM0319 datasheet(317/368 Pages) STMICROELECTRONICS

317 / 368 page

RM0319

System controller (SYSCTR)

Doc ID 022640 Rev 3

317/368

29.3.1

System modes control

Here there is a description of how the system controller changes between modes: DOZE,

SLEEP, SLOW and NORMAL.

The state machine is controlled using three mode control bits (ModeCtrl[2:0]) in the system

control register (SCCTRL), which define the required system operating mode. The mode

control bits control the modes:

●

1xx If the most significant bit (MSB) is set then the system moves into NORMAL mode.

●

01x If the MSB is not set and the next MSB is set then the system moves into SLOW

mode.

●

001 If only the least significant bit (LSB) is set then the system moves into DOZE mode.

●

000 If none of the mode control bits are set the system moves into SLEEP mode.

When the required operating mode has been defined in the system mode control register

the system mode control state machine moves to the required operating mode without

further software interaction.

The current system mode can read by software from the ModeStatus[3:0] bits in the

SCCTRL register.

If the nPOR input is activated, the state machine and the required operating mode in the

system control register are set to DOZE. If the PRESETn input is activated, the system

mode control state machine does not change mode but the required operating mode is set

to DOZE in the system control register.

SLEEP mode

During this mode the system clocks, HCLK and CLK, are disabled and the system controller

clock SCLK is driven from a low speed oscillator (nominally 32 768 Hz). When either a FIQ

or an IRQ interrupt is activated (through the VIC) the system moves into the DOZE mode.

Additionally, the required operating mode in the system control register automatically

changes from SLEEP to DOZE.

DOZE mode

During this mode the system clocks, HCLK and CLK, and the system controller clock SCLK

are driven from the output of crystal oscillator (24 MHz) or low frequency oscillator (32 kHz).

The system controller moves into SLEEP mode from DOZE mode only when none of the

mode control bits are set and the processor is in Wait-for-interrupt state. If SLOW mode or

NORMAL mode is required the system moves into the XTAL control transition state to

initialize the crystal oscillator.

SLOW mode

During this mode, both the system clocks and the system controller clock are driven from

the output of the crystal oscillator.

If NORMAL mode is required, the system moves into the “PLL control” transition state. If

neither the SLOW nor the NORMAL mode control bits are set, the system moves into the

“Switch from XTAL” transition state.

NORMAL mode

In NORMAL mode, both the system clocks and the system controller clock are driven from

the output of PLL.

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