NEC PD750008 User Manual
223
CHAPTER 7 STANDBY FUNCTION
<Sample program>
(Initialization)
MOV
A,#0011B
MOV
PCC,A
; High-speed mode
MOV
XA,#05
MOV
WM,XA
; Subsystem clock
EI
IE4
EI
IEW
EI
; Enable interrupt
(Main routine)
SKT
PORT0.0
; Power normal?
HALT
; Power-down mode
NOP
; Power normal?
SKTCLR
IRQW
; Flag set for 0.5 second?
BR
MAIN
; NO
CALL
WATCH
; Clock subroutine
MAIN:
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(INT4 service routine)
VINT4:
SKT
PORT0.0
; Power normal? MBE = 0
BR
PDOWN
CLR1
SCC.3
; Start main system clock oscillation
MOV
A,#8
MOV
BTM,A
WAIT1:
SKT
IRQBT
; Wait for 250 ms
BR
WAIT1
SKT
PORT0.0
; Chattering check
BR
PDOWN
CLR1
SCC.0
; Switch to main system clock
RETI
PDOWN:
SET1
SCC.0
; Switch to subsystem clock
MOV
A,#6
WAIT2:
INCS
A
; Wait for 32 machine cycles
BR
WAIT2
SET1
SCC.3
; Stop main system clock oscillation
RETI
Caution Before the system clock is changed from the main system clock to the subsystem clock,
a wait time sufficient for stable subsystem clock generation is required.