TMP86FS49BUG Datasheet, PDF (56/294 Pages) Toshiba Semiconductor – 8 Bit Microcontroller

3. Interrupt Control Circuit
3.3 Interrupt Sequence
TMP86FS49BUG
A maskable interrupt is not accepted until the IMF is set to “1” even if the maskable interrupt higher than the
level of current servicing interrupt is requested.
In order to utilize nested interrupt service, the IMF is 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 shorten compared with length
between interrupt requests; otherwise the status cannot be recovered as non-maskable interrupt would simply
nested.
3.3.2 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 accumulator and others are not. These registers are
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.
3.3.2.1 Using PUSH and POP instructions
If only a specific register is saved or interrupts of the same source are nested, general-purpose registers
can be saved/restored using the PUSH/POP instructions.
Example :Save/store register using PUSH and POP instructions
PINTxx:
PUSH
WA
; Save WA register
(interrupt processing)
POP
WA
; Restore WA register
RETI
; RETURN
SP
PCL
PCH
PSW
At acceptance of
an interrupt
SP
A
W
PCL
PCH
PSW
At execution of
PUSH instruction
SP
PCL
PCH
PSW
At execution of
POP instruction
Address
(Example)
b-5
b-4
b-3
b-2
b-1
SP
b
At execution of
RETI instruction
Figure 3-3 Save/store register using PUSH and POP instructions
3.3.2.2 Using data transfer instructions
To save only a specific register without nested interrupts, data transfer instructions are available.
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