ST72321BXXX-AUTO Datasheet, PDF (71/247 Pages) STMicroelectronics – 8-bit MCU for automotive with 32 to 60 Kbyte Flash/ROM, ADC, 5 timers, SPI, SCI, I2C interface

ST72321Bxxx-Auto
Power saving modes
Figure 26. Active Halt mode flowchart
HALT INSTRUCTION
(MCCSR.OIE = 1)
N
INTERRUPT
Y
OSCILLATOR
PERIPHERALS⁽¹⁾
CPU
I[1:0] BITS
ON
OFF
OFF
10
N
RESET
Y
OSCILLATOR
PERIPHERALS
CPU
I[1:0] BITS
ON
OFF
ON
XX⁽²⁾
256 OR 4096 CPU CLOCK
CYCLE DELAY
OSCILLATOR
PERIPHERALS
CPU
I[1:0] BITS
ON
ON
ON
XX⁽²⁾
FETCH RESET VECTOR
OR SERVICE INTERRUPT
8.4.2
1. Peripheral clocked with an external clock source can still be active.
2. Before servicing an interrupt, the CC register is pushed on the stack. The I[1:0] bits of the CC register are
set to the current software priority level of the interrupt routine and restored when the CC register is
popped.
Halt mode
The Halt mode is the lowest power consumption mode of the MCU. It is entered by
executing the ‘HALT’ instruction when the OIE bit of the Main Clock Controller Status
register (MCCSR) is cleared (see Chapter 11: Main clock controller with real-time clock and
beeper (MCC/RTC) for more details on the MCCSR register).
The MCU can exit Halt mode on reception of either a specific interrupt (see Table 19:
Interrupt mapping on page 62) or a RESET. When exiting Halt mode by means of a RESET
or an interrupt, the oscillator is immediately turned on and the 256 or 4096 CPU cycle delay
is used to stabilize the oscillator. After the start up delay, the CPU resumes operation by
servicing the interrupt or by fetching the reset vector which woke it up (see Figure 28).
When entering Halt mode, the I[1:0] bits in the CC register are forced to ‘10b’ to enable
interrupts. Therefore, if an interrupt is pending, the MCU wakes up immediately.
In Halt mode, the main oscillator is turned off causing all internal processing to be stopped,
including the operation of the on-chip peripherals. All peripherals are not clocked except the
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