ST92196A STMicroelectronics, ST92196A Datasheet - Page 50

• Manufacturer Part Number: ST92196A
• Description: 8/16-bit Mcu For Tv Applications With Up To 96k Rom, On-screen-display And 1 Or 2 Data Slicers
• Manufacturer: STMicroelectronics

ARBITRATION MODES (Cont’d)
End of Interrupt Routine
The iret Interrupt Return instruction executes
the following steps:
– The Flag register is popped from system stack.
– If ENCSR is set, CSR is popped from system
– The PC high byte is popped from system stack.
– The PC low byte is popped from system stack.
– All unmasked Interrupts are enabled by setting
– The priority level of the interrupted routine is
Figure 22. Complex Example of a Sequence of Interrupt Requests with:
- Nested mode
- IEN set to 1 during the interrupt routine execution
Priority Level of
Interrupt Request
0
1
2
3
4
5
6
7
stack.
the CICR.IEN bit.
popped from the special register (NICR) and
copied into CPL.
CPL is set to 7
INT5
MAIN
ei
CPL=5
INT 5
INT2
INT3
INT4
ei
CPL=2
INT0
INT 2
ei
CPL2 < CPL4:
Serviced just after ei
CPL=0
INT 0
CPL=2
INT 2
ei
CPL6 > CPL3:
INT6 pending
CPL=3
INT 3
INT6
CPL=4
INT 4
INT2
ei
– If ENCSR is reset, CSR is used instead of ISR,
The suspended routine thus resumes at the inter-
rupted instruction.
Figure 21
if the ei instruction is not used in the interrupt
service routines, nested and concurrent modes
are equivalent.
Figure 22
showing how nested mode allows nested interrupt
processing (enabled inside the interrupt service
routinesi using the ei instruction) according to
their priority level.
CPL=2
INT 2
unless the program returns to another nested
routine.
CPL=4
INT 4
contains a simple example, showing that
contains a more complex example
CPL=5
INTERRUPT 0 HAS PRIORITY LEVEL 0
INTERRUPT 2 HAS PRIORITY LEVEL 2
INTERRUPT 3 HAS PRIORITY LEVEL 3
INTERRUPT 4 HAS PRIORITY LEVEL 4
INTERRUPT 5 HAS PRIORITY LEVEL 5
INTERRUPT 6 HAS PRIORITY LEVEL 6
INT 5
CPL=6
INT 6
MAIN
CPL=7
INTERRUPTS
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