NEC PD750008 - Manual (Page 225)

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CHAPTER 6 INTERRUPT AND TEST FUNCTIONS
(3) Nesting of interrupts with higher priority (INTBT has higher priority and INTT0 and INTCSI have
lower priority)
<1> INTBT is specified as having the higher priority by setting of IPS, and the interrupt is enabled at the
same time.
<2> INTT0 service program is started when INTT0 with the lower priority occurs. Status 1 is set and the
other interrupts with the lower priority are disabled. RBE = 0 to select register bank 0.
<3> INTBT with the higher priority occurs. The level-two interrupts occurs. The status is changed to 0
and all the interrupts are disabled.
<4> RBE = 1 and RBS = 1 to select register bank 1 (only the registers used may be saved by the PUSH
instruction).
<5> RBS is returned to 2, and execution returns to the main program. The status is returned to 1.
Reset
Status 0
<INTT0 service program>
Status 0
Status 1
; RBE = 1, MBE = 0
SEL
EI
EI
EI
MOV
MOV RB2
IEBT
IET0
IECSI
A, #9
IPS, A
<1>
<2> INTT0
<5>
RETI
; RBE = 0
Status 1
<4>
; RBE = 1
SEL RB1
SEL RB2
RETI
Status 2
<INTBT service program>
<3> INTBT
*