Datasheet

 2010-2013 Microchip Technology Inc. DS20002266E-page 29
MCP79410/MCP79411/MCP79412
8.6.1 POWER-DOWN TIME-STAMP
REGISTERS
The MCP7941X family of RTCC devices feature a
power-fail time-stamp feature. This feature will store
the time at which VCC crosses the VTRIP voltage and is
shown in Figure 8-6. To use this feature, a V
BAT
supply must be present and the oscillator must also be
running. The month through minutes are saved.
There are two separate sets of registers that are used
to record this information:
• The first set, located at 0x18 through 0x1B, is
loaded at the time when V
CC falls below VTRIP
and the RTCC operates on the V
BAT. The VBAT
(Day register bit 4) bit is also set at this time.
• The second set of registers, located at 0x1C
through 0x1F, is loaded at the time when V
CC is
restored and the RTCC switches to V
CC.
The power-fail time-stamp registers are cleared when
the VBAT (Day register bit 4) bit is cleared in software.
Only the first power-down and power-up time-stamps
are saved by the RTCC.
FIGURE 8-6: POWER-FAIL GRAPH
VCC
V
TRIP(max)
V
TRIP(min)
TFVCC
TRVC
C
Power-Down
Power-Up
Time Stamp
Time Stamp
Note: It is strongly recommended that the time saver function only be used when the oscillator is running. This
will ensure accurate functionality.