ST72561XX Datasheet, PDF (50/324 Pages) STMicroelectronics – Clock, reset and supply management

Interrupts
6
Interrupts
ST72561-Auto
6.1
Introduction
The ST7 enhanced interrupt management provides the following features:
● Hardware interrupts
● Software interrupt (TRAP)
● Nested or concurrent interrupt management with flexible interrupt priority and level
management:
– Up to 4 software programmable nesting levels
– Up to 16 interrupt vectors fixed by hardware
– 2 non maskable events: RESET, TRAP
– 1 maskable Top Level Event: TLI
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 high addresses of the memory map
(FFE0h to FFFFh) sorted by hardware priority order.
This enhanced interrupt controller guarantees full upward compatibility with the standard
(not nested) ST7 interrupt controller.
6.2
Note:
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
Table 12). The processing flow is shown in Figure 17.
When an interrupt request 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.
● I1 and I0 bits of CC register are set according to the corresponding values in the ISPRx
registers of the serviced interrupt vector.
● 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 “Interrupt Mapping” table
for vector addresses).
The interrupt service routine should end with the IRET instruction which causes the
contents of the saved registers to be recovered from the stack.
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.
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