MEC1404 Datasheet, PDF (312/572 Pages) Microchip Technology – Keyboard and Embedded Controller Products for Notebook PC

MEC140X/1X
21.9 Description
The RTC/Week Alarm block provides battery-powered timekeeping functions, derived from a low-power 32KHz clock,
that operate even when the device’s main power is off. The block contains a set of counters that can be used to generate
one-shot and periodic interrupts to the EC for periods ranging from about 30 microseconds to over 8 years. The
RTC/Week Alarm can be used in conjunction with the VBAT-Powered Control Interface to power up a sleeping system
after a configurable period.
In addition to basic timekeeping, the RTC/Week Alarm block can be used to control the battery-powered general pur-
pose BGPO outputs.
21.9.1 INTERNAL COUNTERS
The RTC/Week Timer includes 3 counters:
21.9.1.1 28-bit Week Alarm Counter
This counter is 28 bits wide. The clock for this counter is the overflow of the Clock Divider, and as long as the RTC/Week
Timer is enabled, it is incremented at a 1 Hz rate.
Both an interrupt and a power-up event can be generated when the contents of this counter matches the contents of the
Week Timer Compare Register.
21.9.1.2 9-bit Sub-Week Alarm Counter
This counter is 9 bits wide. It is decremented by 1 at each tick of its selected clock. It can be configured either as a one-
shot or repeating event generator.
Both an interrupt and a power-up event can be generated when this counter decrements from 1 to 0.
The Sub-Week Alarm Counter can be configured with a number of different clock sources for its time base, derived from
either the Week Alarm Counter or the Clock Divider, by setting the SUBWEEK_TICK field of the Sub-Week Control Reg-
ister.
TABLE 21-7:
SUBWEEK_
TICK
0
1
2
3
4
SUB-WEEK ALARM COUNTER CLOCK
Source
SPISR
Frequency
Minimum
Duration
Sub-Second
Second
Week Counter
bit 3
Counter Disabled
0
Counter Disabled
1
2 Hz
500 ms
2
4 Hz
250 ms
3
8 Hz
125 ms
4
16 Hz
62.5
5
32 Hz
31.25 ms
6
64 Hz
15.6 ms
7
128 Hz
7.8 ms
8
256 Hz
3.9 ms
9
512 Hz
1.95 ms
10
1024 Hz
977 µS
11
2048 Hz
488 µS
12
4096 Hz
244 µS
13
8192 Hz
122 µS
14
16.384 Khz
61.1 µS
15
32.768 KHz
30.5 µS
n/a
1 Hz
1 sec
Reserved
n/a
125 Hz
8 sec
Maximum
Duration
255.5 sec
127.8 sec
63.9 sec
31.9 sec
16.0 sec
8 sec
4 sec
2 sec
1 sec
499 ms
249.5 ms
124.8 ms
62.4 ms
31.2 ms
15.6 ms
511 sec
68.1 min
DS00001956D-page 312
 2015 - 2016 Microchip Technology Inc.