TMP89FS60 datasheet(71/410 Pages) TOSHIBA

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Page 57

TMP89FS60

RA003

A maskable interrupt is not accepted until the IMF is set to “1” even if the maskable interrupt is requested in

the interrupt service routine.

In order to utilize nested interrupt service, the IMF must be set to “1” in the interrupt service program. In this

case, acceptable interrupt sources are selectively enabled by the individual interrupt enable flags.

To avoid overloaded nesting, clear the individual interrupt enable flag whose interrupt is currently serviced,

before setting IMF to “1”. As for non-maskable interrupt, keep interrupt service shorter compared with length

between interrupt requests.

3.5.3

Saving/restoring general-purpose registers

During interrupt acceptance processing, the program counter (PC) and the program status word (PSW,

includes IMF) are automatically saved on the stack, but the general purpose registers are not. These registers

must be saved by software if necessary. When multiple interrupt services are nested, it is also necessary to

avoid using the same data memory area for saving registers. The following methods are used to save/restore the

general-purpose registers.

3.5.3.1

Using PUSH and POP instructions

To save only a specific register, PUSH and POP instructions are available.

Figure 3-3 Saving/restoring general-purpose registers

Example :Using PUSH and POP instructions

PINTxx

PUSH

; Save WA register

Interrupt processing

POP

; Restore WA register

RETI

; RETURN

At Acceptance of

an Interrupt

PSW

PCL

PCH

Address

(Example)

b-4

b-3

b-2

b-1

PSW

PCL

PCH

At execution of

PUSH instruction

At execution of

POP instruction

At execution of

an RETI instruction

PSW

PCL

PCH

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