MCP795WXX/MCP795BXX
Description:
The MCP795XXX is a low-power Real-Time Clock/
Calendar (RTCC) that uses digital trimming compen-
sation for an accurate clock/calendar, an interrupt out-
put to support alarms and events, a power sense
circuit that automatically switches to the backup sup-
ply, non-volatile memory for safe data storage and
several enhanced features that support system
requirements.
Along with a low-cost 32,768 kHz crystal, this RTCC
tracks time using several internal registers and then
communicates the data over a 10 MHz SPI bus that is
fast enough to support a programmable millisecond
alarm.
The device is fully accessible through the serial inter-
face, while V
CC
is between 1.8V and 5.5V, but can
operate down to 1.3V through the backup supply con-
nected to the V
BAT
input for timekeeping and SRAM
retention only.
As part of the power sense circuit, a time saver
function is implemented to store the time when main
power is lost and again, when power is restored to log
the duration of a power failure.
Along with the onboard serial EEPROM and battery-
backed SRAM, a 128-bit protected space is available
for a unique ID. This space can be ordered
preprogrammed with a MAC address, or blank for the
user to program.
This clock/calendar automatically adjusts for months
with fewer than 31 days including corrections for leap
years. The clock operates in either 24-hour or 12-hour
format with AM/PM indicator and settable alarm(s).
Using the external crystal, the CLKOUT pin can be set
to generate a number of output frequencies. In
addition, the MCP795BXX devices support a 32 kHz
clock output at power-up on the CLKOUT/BOOT pin
by using the same crystal driving the RTCC device.
For versatility, a digital event detect with a
programmable pulse count can identify the 1
st
, 4
th
,
16
th
or 32
nd
pulse before sending an interrupt. A
second event detect with built-in debounce input filter
was also implemented to support noisy mechanical
switches.
Since many microcontrollers do not have an integrated
Watchdog Timer, this peripheral has been imple-
mented in the RTCC. For many applications, this
function must be performed outside the microcontroller
for increased robustness.
FIGURE 1-1:
BLOCK DIAGRAM
X1
OSC
X2
V
BAT
SWITCHOVER
CLKOUT Divider
Vcc
CLKOUT/
BOOT
V
BAT
EVHS
EVENT
DETECT
EEPROM
/WDO
ID
/IRQ
WDT
SRAM
/CS
ALARMS
SPI
EVLS
SCK
TIME-STAMP
SI
Vss
SO
DS22280A-page 2
Preliminary
2011 Microchip Technology Inc.
MAS [ MICRO ANALOG SYSTEMS ]
