User`s manual

BL1600126 s Power Management
ADM691 Power Supervisor
The ADM691 power-supervisor IC (U13) helps the system survive power
fluctuations and outages. It provides these vital services.
 Power-on reset.
The ADM691 generates the power-on reset for the BL1600 by holding
/RESET low until the ICs internal comparators sense that VCC has
risen above 4.65 V (the ICs preset reset threshold ).
 RAM protection
The ADM691 gates the decoded RAM-select line, /RAMCEIN, to the
RAMs chip-enable line, /RAMCE, whenever VCC is above the reset
threshold and VBAT. When VCC falls below the threshold, the
ADM691 deasserts /RAMCE to prevent spurious writing to the RAM.
 Watchdog timer
The ADM691 provides a watchdog timer that guards against system or
software faults by resetting the BL1600 if the software does not hit
the watchdog timer input, WDI, at least every 1.0 seconds. Hit the
watchdog timer by calling the function hitwd.
The supervisors watchdog output, /WDO, connects to the Z180s RXS/
CTSI- interrupt line; /WDO is at a logic zero level after a watchdog
reset and a logic 1 after a power-on reset.
 Nonmaskable interrupt
The ADM691 generates a nonmaskable interrupt, /NMI, from its
power-fail output, /PFO, if the unregulated DC input, normally 9 V to
12 V DC, falls below 7.9 V, giving the BL1600 advanced warning of an
impending power failure so that it can execute shutdown routines. The
voltage divider, R1-R2, determines this 7.9 V level.
/NMI also connects to the Z180 via multiplexer U2 to allow your
software to monitor the /NMI line after the nonmaskable interrupt, and
to recover from temporary low-input voltage conditions or brown-
outs.
 Backup-battery switchover
The ADM691 switches the RAM over to battery power if VCC falls
below the batterys voltage