ST72321AR9-Auto STMicroelectronics, ST72321AR9-Auto Datasheet - Page 36

• Manufacturer Part Number: ST72321AR9-Auto
• Description: 8-bit MCU for automotive with 60 Kbyte Flash, 10-bit ADC, timers, SPI, SCI and I2C interfaces
• Manufacturer: STMicroelectronics

Specifications of ST72321AR9-Auto

• Hdflash Endurance: 100 cycles, data retention 20 years
• Clock Sources: crystal/ceramic resonator oscillators, internal RC oscillator and bypass for external clock
• 4 Power Saving Modes: Halt, Active Halt, Wait and Slow

Central processing unit (CPU)
Note:
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The stack pointer is a 16-bit register which is always pointing to the next free location in the
stack. It is then decremented after data has been pushed onto the stack and incremented
before data is popped from the stack (see
Since the stack is 256 bytes deep, the 8 most significant bits are forced by hardware.
Following an MCU Reset, or after a reset stack pointer instruction (RSP), the stack pointer
contains its reset value (the SP7 to SP0 bits are set) which is the stack higher address.
The least significant byte of the stack pointer (called S) can be directly accessed by an LD
instruction.
When the lower limit is exceeded, the stack pointer wraps around to the stack upper limit,
without indicating the stack overflow. The previously stored information is then overwritten
and therefore lost. The stack also wraps in case of an underflow.
The stack is used to save the return address during a subroutine call and the CPU context
during an interrupt. The user may also directly manipulate the stack by means of the PUSH
and POP instructions. In the case of an interrupt, the PCL is stored at the first location
pointed to by the SP. The other registers are then stored in the next locations as shown in
Figure
●
●
A subroutine call occupies two locations and an interrupt five locations in the stack area.
Figure 8.
@ 0100h
@ 01FFh
SP
When an interrupt is received, the SP is decremented and the context is pushed on the
stack.
On return from interrupt, the SP is incremented and the context is popped from the
stack.
8.
Subroutine
Stack Higher Address = 01FFh
Stack Lower Address = 0100h
CALL
PCH
PCL
Stack manipulation example
SP
Interrupt
Event
PCH
PCH
PCL
PCL
CC
A
X
Doc ID 13829 Rev 1
SP
PUSH Y
PCH
PCH
PCL
PCL
CC
Y
A
X
Figure
SP
8).
POP Y
PCH
PCH
PCL
PCL
CC
A
X
SP
IRET
PCH
PCL
ST72321xx-Auto
SP
or RSP
RET