ST72325 Datasheet, PDF (39/193 Pages) STMicroelectronics – 8-BIT MCU WITH 16 TO 60K FLASH/ROM, ADC, CSS, FIVE TIMERS, SPI, SCI, I2C INTERFACE

ST72325
INTERRUPTS (Cont’d)
7.5 INTERRUPT REGISTER DESCRIPTION
CPU CC REGISTER INTERRUPT BITS
Read / Write
Reset Value: 111x 1010 (xAh)
7
0
1
1
I1
H
I0
N
Z
C
Bit 5, 3 = I1, I0 Software Interrupt Priority
These two bits indicate the current interrupt soft-
ware priority.
Interrupt Software Priority Level I1
I0
Level 0 (main)
Low
1
0
Level 1
0
1
Level 2
0
0
Level 3 (= interrupt disable*) High 1
1
These two bits are set/cleared by hardware when
entering in interrupt. The loaded value is given by
the corresponding bits in the interrupt software pri-
ority registers (ISPRx).
They can be also set/cleared by software with the
RIM, SIM, HALT, WFI, IRET and PUSH/POP in-
structions (see “Interrupt Dedicated Instruction
Set” table).
*Note: TRAP and RESET events can interrupt a
level 3 program.
INTERRUPT SOFTWARE PRIORITY REGIS-
TERS (ISPRX)
Read/Write (bit 7:4 of ISPR3 are read only)
Reset Value: 1111 1111 (FFh)
7
0
ISPR0 I1_3 I0_3 I1_2 I0_2 I1_1 I0_1 I1_0 I0_0
ISPR1 I1_7 I0_7 I1_6 I0_6 I1_5 I0_5 I1_4 I0_4
ISPR2 I1_11 I0_11 I1_10 I0_10 I1_9 I0_9 I1_8 I0_8
ISPR3 1 1 1 1 I1_13 I0_13 I1_12 I0_12
These four registers contain the interrupt software
priority of each interrupt vector.
– Each interrupt vector (except RESET and TRAP)
has corresponding bits in these registers where
its own software priority is stored. This corre-
spondance is shown in the following table.
Vector address
FFFBh-FFFAh
FFF9h-FFF8h
...
FFE1h-FFE0h
ISPRx bits
I1_0 and I0_0 bits*
I1_1 and I0_1 bits
...
I1_13 and I0_13 bits
– Each I1_x and I0_x bit value in the ISPRx regis-
ters has the same meaning as the I1 and I0 bits
in the CC register.
– Level 0 can not be written (I1_x=1, I0_x=0). In
this case, the previously stored value is kept. (ex-
ample: previous=CFh, write=64h, result=44h)
The TLI, RESET, and TRAP vectors have no soft-
ware priorities. When one is serviced, the I1 and I0
bits of the CC register are both set.
*Note: Bits in the ISPRx registers which corre-
spond to the TLI can be read and written but they
are not significant in the interrupt process man-
agement.
Caution: If the I1_x and I0_x bits are modified
while the interrupt x is executed the following be-
haviour has to be considered: If the interrupt x is
still pending (new interrupt or flag not cleared) and
the new software priority is higher than the previ-
ous one, the interrupt x is re-entered. Otherwise,
the software priority stays unchanged up to the
next interrupt request (after the IRET of the inter-
rupt x).
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