Z-World OP7100, User Manual

Page: 27 / 122

OP7100 Hardware s 27
main(){
...
}
...
char dummy[24];
...
#define NMI_BIT
0 ; bit 0
#JUMP_VEC NMI_VEC myint
#asm
myint::
ld sp,dummy+24 ; force stack pointer
; to top of dummy vector
; to prevent overwriting
; code or data
do whatever service, within allowable execution time
loop:
call hitwd ; make sure no watchdog reset
; while low voltage
ld bc,NMI ; load the read NMI register
; to bc
in a,(c) ; read the read NMI register
; for /PFO
bit NMI_BIT, a ; check for status of /PFO
jr z,loop ; wait until the brownout
; clears
timeout: ; then...a tight loop to
; force a watchdog timeout,
jp timeout ; resetting the Z180
#endasm
Of course, if the
DC
input voltage continues to decrease, then the OP7100
will just power down.
Call the Dynamic C function
hitwd
during the power-failure service
routine to make sure that the watchdog timer does not time out and thereby
reset the processor. The controller can continue to run at low voltages, and
so it might not be able to detect the low-voltage condition after the
watchdog timer resets the processor.
Watchdog Timer
To increase reliability, the ADM691’s watchdog timer forces a system reset if
a program does not notify the supervisor nominally at least every second. The
assumption is that if the program fails to “hit” the watchdog, the program
must be stuck in a loop or halted. The Dynamic C function for hitting the