ST STM32F40 Series Reference Manual page 1397

Debug support (DBG)
31 30 29
15 14 13
Bits 31:8 Reserved, must be kept at reset value.
Bits 7:5 TRACE_MODE[1:0] and TRACE_IOEN: Trace pin assignment control
– With TRACE_IOEN=0:
– With TRACE_IOEN=1:
Bits 4:3 Reserved, must be kept at reset value.
Bit 2 DBG_STANDBY: Debug Standby mode
Bit 1 DBG_STOP: Debug Stop mode
Bit 0 DBG_SLEEP: Debug Sleep mode
1397/1422
28 27 26 25
12 11 10 9
Reserved
TRACE_MODE=xx: TRACE pins not assigned (default state)
– TRACE_MODE=00: TRACE pin assignment for Asynchronous Mode
– TRACE_MODE=01: TRACE pin assignment for Synchronous Mode with a
TRACEDATA size of 1
– TRACE_MODE=10: TRACE pin assignment for Synchronous Mode with a
TRACEDATA size of 2
– TRACE_MODE=11: TRACE pin assignment for Synchronous Mode with a
TRACEDATA size of 4
0: (FCLK=Off, HCLK=Off) The whole digital part is unpowered.
From software point of view, exiting from Standby is identical than fetching reset vector
(except a few status bit indicated that the MCU is resuming from Standby)
1: (FCLK=On, HCLK=On) In this case, the digital part is not unpowered and FCLK and
HCLK are provided by the internal RC oscillator which remains active. In addition, the MCU
generate a system reset during Standby mode so that exiting from Standby is identical than
fetching from reset
0: (FCLK=Off, HCLK=Off) In STOP mode, the clock controller disables all clocks (including
HCLK and FCLK). When exiting from STOP mode, the clock configuration is identical to the
one after RESET (CPU clocked by the 8 MHz internal RC oscillator (HSI)). Consequently,
the software must reprogram the clock controller to enable the PLL, the Xtal, etc.
1: (FCLK=On, HCLK=On) In this case, when entering STOP mode, FCLK and HCLK are
provided by the internal RC oscillator which remains active in STOP mode. When exiting
STOP mode, the software must reprogram the clock controller to enable the PLL, the Xtal,
etc. (in the same way it would do in case of DBG_STOP=0)
0: (FCLK=On, HCLK=Off) In Sleep mode, FCLK is clocked by the system clock as previously
configured by the software while HCLK is disabled.
In Sleep mode, the clock controller configuration is not reset and remains in the previously
programmed state. Consequently, when exiting from Sleep mode, the software does not
need to reconfigure the clock controller.
1: (FCLK=On, HCLK=On) In this case, when entering Sleep mode, HCLK is fed by the same
clock that is provided to FCLK (system clock as previously configured by the software).
Doc ID 018909 Rev 4
24 23 22 21
Reserved
8 7 6 5
TRACE_ TRACE
MODE _
[1:0] IOEN
rw rw rw
20 19 18 17
4 3 2 1
DBG_
DBG_
STAND
STOP
Reserved
BY
rw rw
RM0090
16
0
DBG_
SLEEP
rw