BS_System controller
RM0082
288/844
Doc ID 018672 Rev 1
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:
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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.
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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 is output on the SYSMODE[3:0] bus and can also be read back by
the processor using the ModeStatus bit 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.
If the NORMAL mode control bit is not set, then the system moves into the “Switch from
PLL” transition state.