User's Manual

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START-UP
Start-up occurs as a result of either crossing the power-on reset threshold or asserting RESETn. After the
completion of power-on reset or the falling edge of an internally synchronized RESETn, WSM2400 loads
its fuse table which, as described in the previous section, includes setting I/O direction. In this state,
WSM2400 checks the state of the FLASH_P_ENn and RESETn and enters the serial flash emulation mode
if both signals are asserted. If the FLASH_P_ENn pin is not asserted but RESETn is asserted, WSM2400
automatically reduces its energy consumption to a minimum until RESETn is released. Once RESETn is
de-asserted, WSM2400 goes through a boot sequence, and then enters the active state.
SERIAL FLASH EMULATION
When both RESETn and FLASH_P_ENn are asserted, WSM2400 disables normal operation and enters a
mode to emulate the operation of a serial flash. In this mode, its flash can be programmed.
OPERATION
Once WSM2400 has completed start-up, WSM2400 transitions to the operational group of states
(active/CPU active, active/ CPU inactive, and Doze). There, WSM2400 cycles between the various states,
automatically selecting the lowest possible power state while fulfilling the demands of network
operation.
ACTIVE STATE
In the active state, WSM2400’s relaxation oscillator is running and peripherals are enabled as needed.
The ARM Cortex-M3 cycles between CPU-active and CPU-inactive (referred to in the ARM Cortex-M3
literature as sleep now mode). WSM2400’s extensive use of DMA and intelligent peripherals that
independently move WSM2400 between active state and doze state minimizes the time the CPU is
active, significantly reducing WSM2400’s energy consumption.
DOZE STATE
The doze state consumes orders of magnitude less current than the active state and is entered when all
of the peripherals and the CPU are inactive. In the doze state WSM2400’s full state is retained, timing is
maintained, and WSM2400 is configured to detect, wake, and rapidly respond to activity on I/Os (such
as UART signals and the TIMEn pin). In the doze state the 32.768kHz oscillator and associated timers are
active.