BQ4845_14 Datasheet, PDF (3/24 Pages) Texas Instruments – Parallel RTC With CPU Supervisor

bq4845/bq4845Y
Pin Descriptions
X1–X2 Crystal inputs
X1–X2 are a direct connection for a
32.768kHZ, 6pF crystal.
RST
Reset output
RST goes low whenever VCC falls below the
power fail threshold. RST will remain low for
200ms typical after VCC crosses the threshold
on power-up. RST also goes low whenever a
watchdog timeout occurs. RST is an open-
drain output.
INT
Interrupt output
INT goes low when a power fail, periodic, or
alarm condition occurs. INT is an open-drain
output.
WDI
Watchdog input
WDI is a three-level input. If WDI remains
either high or low for longer than the
watchdog time-out period (1.5 seconds de-
fault), WDO goes low. WDO remains low
until the next transition at WDI. Leaving
WDI unconnected disables the watchdog
function. WDI connects to an internal volt-
age divider between VOUT and VSS, which
sets it to mid-supply when left uncon-
nected.
WDO
Watchdog output
WDO goes low if WDI remains either high
or low longer than the watchdog time-out
period. WDO returns high on the next tran-
sition at WDI. WDO remains high if WDI is
unconnected.
A0–A3
Clock address inputs
A0–A3 allow access to the 16 bytes of real-
time clock and control registers.
DQ0–DQ7 Data input and output
DQ0–DQ7 provide x8 data for real-time clock
information. These pins connect to the mem-
ory data bus.
VSS
Ground
CS
Chip select
OE
Output enable
OE provides the read control for the RTC
memory locations.
CEOUT Chip enable output
CEOUT goes low only when CEIN is low and
VCC is above the power fail threshold. If
CEIN is low, and power fail occurs, CEOUT
stays low for 100µs or until CEIN goes high,
whichever occurs first.
CEIN
Chip enable input
CEIN is the input to the chip-enable gating
circuit.
BC
Backup battery input
BC should be connected to a 3V backup
cell. A voltage within the VBC range on the
BC pin should be present upon power up to
provide proper oscillator start-up.
VOUT
Output supply voltage
VOUT provides the higher of VCC or VBC,
switched internally, to supply external
RAM.
WE
Write enable
WE provides the write control for the RTC
memory locations.
VCC
Input supply voltage
+5V input
Aug. 1995
3