M30201 datasheet(39/172 Pages) RENESAS

39 / 172 page

Mitsubishi microcomputers

M30201 Group

SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER

Interrupts

Saving Registers

In the interrupt sequence, only the contents of the flag register (FLG) and that of the program counter

(PC) are saved in the stack area.

First, the processor saves the 4 high-order bits of the program counter, and 4 high-order bits and 8 low-

order bits of the FLG register, 16 bits in total, in the stack area, then saves 16 low-order bits of the

program counter. Figure 1.27 shows the state of the stack as it was before the acceptance of the interrupt

request, and the state the stack after the acceptance of the interrupt request.

Save other necessary registers at the beginning of the interrupt routine using software. Using the

PUSHM instruction alone can save all the registers except the stack pointer (SP).

Figure 1.27. State of stack before and after acceptance of interrupt request

Address

Content of previous stack

Stack area

[SP]

Stack pointer

value before

interrupt occurs

m – 1

m – 2

m – 3

m – 4

Stack status before interrupt request

is acknowledged

Stack status after interrupt request

is acknowledged

Content of previous stack

m + 1

MSB

LSB

m – 1

m – 2

m – 3

m – 4

Address

Flag register (FLGL)

Content of previous stack

Stack area

Flag register

(FLGH)

Program

counter (PCH)

[SP]

New stack

pointer value

Content of previous stack

m + 1

MSB

LSB

Program counter (PCL)

Program counter (PCM)

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