Toshiba TLCS-870/C1 Series, Manual

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TMP89FM42
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 WA ; Save WA register
Interrupt processing
POP WA ; Restore WA register
RETI ; RETURN
At Acceptance of
an Interrupt
PSW
SP
PC
L
PC
H
Address
(Example)
b-4
b-3
b-2
b-1
b PSW
SP
PC
L
PC
H
At execution of
PUSH instruction
At execution of
POP instruction
SP
At execution of
an RETI instruction
PSW
W
A
SP
PC
L
PC
H