7702 datasheet(65/217 Pages) RENESAS

65 / 217 page

7702/7703 Group User’s Manual

4–3

INTERRUPTS

When an interrupt request is accepted, the contents of the registers listed below immediately preceding the

acceptance of the interrupt request are automatically saved to the stack area in order of registers

→→.

Program bank register (PG)

Program counter (PCL, PCH)

Processor status register (PSL, PSH)

Figure 4.1.2 shows the state of the stack area just before entering the interrupt routine.

Execute the RTI instruction at the end of this interrupt routine to return to the routine that the microcomputer

was executing before the interrupt request was accepted. As the RTI instruction is executed, the register

contents saved in the stack area are restored in order of registers

→→, and a return is made to the

routine executed before the acceptance of interrupt request and processing is resumed from it.

When an interrupt request is accepted and the RTI instruction is executed, the only above registers to

are automatically saved and restored. When there are any other registers of which contents are necessary

to be kept, use software to save and restore them.

Fig. 4.1.2 State of stack area just before entering interrupt routine

4.1 Overview

[S] is an initial value that the stack pointer (S) indicates at

accepting an interrupt request. The S’s contents become

[S] – 5 after saving the above registers.

Address

[S] – 4

[S] – 3

[S] – 2

[S] – 1

[S]V

Processor status register’s low-order byte (PSL)

Stack area

[S] – 5

Processor status register’s high-order byte (PSH)

Program counter’s low-order byte (PCL)

Program counter’s high-order byte (PCH)

Program bank register (PG)

7702 Datasheet(PDF) 65 Page - Renesas Technology Corp