Panasonic MN101C77C PC bits 16-9 → SP+2, PC bits 8-1 → SP+1, Psw →, Interrupt mask IMn in the PSW

during interrupt acceptance

Chapter 3 Interrupts

■Interrupt Acceptance Operation

When accepting an interrupt, this LSI hardware saves the handy address register, the return address from the program counter, and the processor status word (PSW) to the stack and branches to the interrupt handler using the starting address in the vector table.

The following is the hardware processing sequence after by interrupt acceptance.

1.The stack pointer (SP) is updated. (SP-6 → SP)

2.The contents of the handy address register (HA) are saved to the stack.

	Upper half of HA →		(SP+5)
	Lower half of HA →		(SP+4)
3.	The contents of the program counter (PC), the return				7			0
	address, are saved to the stack.
	PC bits 18, 17, and 0 → (SP+3)			New SP		PSW			Lower
	PC bits 16-9 →	(SP+2)		(after interrupt		PC8 - 1
				acceptance)
	PC bits 8-1 →	(SP+1)
						PC16 - 9
									Address
4.	The contents of the PSW are saved to the stack.					PC0 Reserved	PC 18,17
	PSW →	(SP)				HA 7 - 0
5.	The interrupt level (xxxLVn) for the interrupt is copied to					HA 15 - 8
									Higher
	the interrupt mask (IMn) in the PSW.			Old SP
				(before interrupt
	Interrupt level (xxxLVn) → IMn
				acceptance)

6.The hardware branches to the address in the vector

table. Figure 3-1-5 Stack Operation

■Interrupt Return Operation

An interrupt handler ends by restoring, using the POP instruction and other means, the contents of any registers used during processing and then executing the return from interrupt (RTI) instruction to return to the point at which execution was interrupted.

The following is the processing sequence after the RTI instruction.

1.The contents of the PSW are restored from the stack. (SP)

2.The contents of the program counter (PC), the return address, are restored from the stack. (SP+1 to SP+3)

3.The contents of the handy address register (HA) are restored from the stack. (SP+4, SP+5)

4. The stack pointer is updated. (SP+6 → SP)

5.Execution branches to the address in the program counter.

The handy address register is an internal register used by the handy addressing function. The hardware saves its contents to the stack to prevent the interrupt from interfering with operation of the function.

Registers such as data register, or address register are not saved, so that PUSH instruction should be used to save data register or address register onto the stack, if neccessary.

The address bp6 to bp2, when program counter (PC) are saved to the stack, are reserved. Do not change by program.

III - 10 Overview