ST7265XEVALMS STMicroelectronics, ST7265XEVALMS Datasheet - Page 38

• Manufacturer Part Number: ST7265XEVALMS
• Manufacturer: STMicroelectronics

Specifications of ST7265XEVALMS

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ST7265x
7 INTERRUPTS
7.1 INTRODUCTION
The CPU enhanced interrupt management pro-
vides the following features:
■
■
■
This interrupt management is based on:
– Bit 5 and bit 3 of the CPU CC register (I1:0),
– Interrupt software priority registers (ISPRx),
– Fixed interrupt vector addresses located at the
This enhanced interrupt controller guarantees full
upward compatibility with the standard (not nest-
ed) CPU interrupt controller.
7.2 MASKING AND PROCESSING FLOW
The interrupt masking is managed by the I1 and I0
bits of the CC register and the ISPRx registers
which give the interrupt software priority level of
each interrupt vector (see
ing flow is shown in
Figure 25. Interrupt Processing Flowchart
38/163
1
high addresses of the memory map (FFE0h to
FFFFh) sorted by hardware priority order.
– Up to 4 software programmable nesting levels
– Up to 16 interrupt vectors fixed by hardware
– 3 non maskable events: RESET, TRAP, TLI
Hardware interrupts
Software interrupt (TRAP)
Nested or concurrent interrupt management
with
management:
flexible
RESTORE PC, X, A, CC
FROM STACK
RESET
interrupt
Figure
Table
25.
priority
8). The process-
Y
and
INSTRUCTION
INTERRUPT
INSTRUCTION
FETCH NEXT
PENDING
EXECUTE
N
“IRET”
N
level
Y
When an interrupt request has to be serviced:
– Normal processing is suspended at the end of
– The PC, X, A and CC registers are saved onto
– I1 and I0 bits of CC register are set according to
– The PC is then loaded with the interrupt vector of
The interrupt service routine should end 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 I1 and I0 bits will be restored from the stack
and the program in the previous level will resume.
Table 8. Interrupt Software Priority Levels
Level 0 (main)
Level 1
Level 2
Level 3 (= interrupt disable)
Interrupt software priority
the current instruction execution.
the stack.
the corresponding values in the ISPRx registers
of the serviced interrupt vector.
the interrupt to service and the first instruction of
the interrupt service routine is fetched (refer to
“Interrupt Mapping” table for vector addresses).
THE INTERRUPT
STAYS PENDING
Interrupt has the same or a
LOAD I1:0 FROM INTERRUPT SW REG.
LOAD PC FROM INTERRUPT VECTOR
lower software priority
than current one
STACK PC, X, A, CC
Level
High
Low
I1:0
TLI
N
I1
1
0
0
1
Y
I0
0
1
0
1