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ST72P63BE1M1 Datasheet(PDF) 27 Page - STMicroelectronics

Part No. ST72P63BE1M1
Description  Low speed USB 8-bit MCU family with up to 32K Flash/ROM, DFU capability, 8-bit ADC, WDG, timer, SCI & I²C
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Maker  STMICROELECTRONICS [STMicroelectronics]
Homepage  http://www.st.com
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ST72P63BE1M1 Datasheet(HTML) 27 Page - STMicroelectronics

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8 Interrupts
The ST7 core may be interrupted by one of two dif-
ferent methods: maskable hardware interrupts as
listed in Table 8, "Interrupt mapping" and a non-
maskable software interrupt (TRAP). The Interrupt
processing flowchart is shown in Figure 19.
The maskable interrupts must be enabled clearing
the I bit in order to be serviced. However, disabled
interrupts may be latched and processed when
they are enabled (see external interrupts subsec-
tion).
When an interrupt has to be serviced:
– Normal processing is suspended at the end of
the current instruction execution.
– The PC, X, A and CC registers are saved onto
the stack.
– The I bit of the CC register is set to prevent addi-
tional interrupts.
– The PC is then loaded with the interrupt vector of
the interrupt to service and the first instruction of
the interrupt service routine is fetched (refer to
Table 8, "Interrupt mapping" for vector address-
es).
The interrupt service routine should finish with the
IRET instruction which causes the contents of the
saved registers to be recovered from the stack.
Note: As a consequence of the IRET instruction,
the I bit will be cleared and the main program will
resume.
Priority management
By default, a servicing interrupt cannot be inter-
rupted because the I bit is set by hardware enter-
ing in interrupt routine.
In the case several interrupts are simultaneously
pending, a hardware priority defines which one will
be serviced first (see Table 8, "Interrupt map-
ping").
Non-maskable software interrupts
This interrupt is entered when the TRAP instruc-
tion is executed regardless of the state of the I bit.
It will be serviced according to the flowchart on
Figure 19.
Interrupts and low power mode
All interrupts allow the processor to leave the Wait
low power mode. Only external and specific men-
tioned interrupts allow the processor to leave the
Halt low power mode (refer to the “Exit from Halt“
column in Table 8, "Interrupt mapping").
External interrupts
The pins ITi/PAk and ITj/PBk (i=1,2; j= 5,6; k=4,5)
can generate an interrupt when a rising edge oc-
curs on this pin. Conversely, the ITl/PAn and ITm/
PBn pins (l=3,4; m= 7,8; n=6,7) can generate an
interrupt when a falling edge occurs on this pin.
Interrupt generation will occur if it is enabled with
the ITiE bit (i=1 to 8) in the ITRFRE register and if
the I bit of the CCR is reset.
Peripheral interrupts
Different peripheral interrupt flags in the status
register are able to cause an interrupt when they
are active if both:
– The I bit of the CC register is cleared.
– The corresponding enable bit is set in the control
register.
If any of these two conditions is false, the interrupt
is latched and thus remains pending.
Clearing an interrupt request is done by one of the
two following operations:
– Writing “0” to the corresponding bit in the status
register.
– Accessing the status register while the flag is set
followed by a read or write of an associated reg-
ister.
Notes:
1. The clearing sequence resets the internal latch.
A pending interrupt (i.e. waiting to be enabled) will
therefore be lost if the clear sequence is executed.
2. All interrupts allow the processor to leave the
Wait low power mode.
3. Exit from Halt mode may only be triggered by an
External Interrupt on one of the ITi ports (PA4-PA7
and PB4-PB7), an end suspend mode Interrupt
coming from USB peripheral, or a reset.


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