STM32W108CBU6 STMICROELECTRONICS [STMicroelectronics], STM32W108CBU6 Datasheet - Page 45

• Manufacturer Part Number: STM32W108CBU6
• Description: High-performance, IEEE 802.15.4 wireless system-on-chip
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

STM32W108CB, STM32W108HB
5.5.3
5.5.4
5.6
In the deep sleep state the STM32W108 waits for a wake up event which will return it to the
running state. In powering up the core logic the ARM® Cortex-M3 is put through a reset
cycle and ST software restores the stack and application state to the point where deep sleep
was invoked.
Further options for deep sleep
By default, the low-frequency internal RC oscillator (OSCRC) is running during deep sleep
(known as deep sleep 1).
To conserve power, OSCRC can be turned off during deep sleep. This mode is known as
deep sleep 2. Since the OSCRC is disabled, the sleep timer and watchdog timer do not
function and cannot wake the chip unless the low-frequency 32.768 kHz crystal oscillator is
used. Non-timer based wake sources continue to function. Once a wake event occurs, the
OSCRC restarts and becomes enabled.
Use of debugger with sleep modes
The debugger communicates with the STM32W108 using the SWJ.
When the debugger is connected, the CDBGPWRUPREQ bit in the debug port in the SWJ
is set, the STM32W108 will only enter deep sleep 0 (the Emulated Deep Sleep state). The
CDBGPWRUPREQ bit indicates that a debug tool is connected to the chip and therefore
there may be debug state in the system debug components. To maintain the state in the
system debug components only deep sleep 0 may be used, since deep sleep 0 will not
cause a power cycle or reset of the core domain. The CSYSPWRUPREQ bit in the debug
port in the SWJ indicates that a debugger wants to access memory actively in the
STM32W108. Therefore, whenever the CSYSPWRUPREQ bit is set while the STM32W108
is awake, the STM32W108 cannot enter deep sleep until this bit is cleared. This ensures the
STM32W108 does not disrupt debug communication into memory.
Clearing both CSYSPWRUPREQ and CDBGPWRUPREQ allows the STM32W108 to
achieve a true deep sleep state (deep sleep 1 or 2). Both of these signals also operate as
wake sources, so that when a debugger connects to the STM32W108 and begins accessing
the chip, the STM32W108 automatically comes out of deep sleep. When the debugger
initiates access while the STM32W108 is in deep sleep, the SWJ intelligently holds off the
debugger for a brief period of time until the STM32W108 is properly powered and ready.
For more information regarding the SWJ and the interaction of debuggers with deep sleep,
contact ST support for Application Notes and ARM® CoreSight documentation.
Security accelerator
The STM32W108 contains a hardware AES encryption engine accessible from the ARM®
Cortex-M3. NIST-based CCM, CCM*, CBC-MAC, and CTR modes are implemented in
hardware. These modes are described in the IEEE 802.15.4-2003 specification, with the
exception of CCM*, which is described in the ZigBee Security Services Specification 1.0.
Doc ID 16252 Rev 2
System modules
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