X1240 Datasheet, PDF (4/19 Pages) Xicor Inc. – Real Time Clock/Calendar with EEPROM

X1240
Table 1. Clock/Control Memory Map
Addr.
Type
Reg
Name
7
6
003F Status
SR
BAT
0
0037
Y2K
0
0
0036
DW
0
0
0035
YR
Y23
Y22
0034
RTC
MO
0
0
0033 ^(SRAM)
DT
0
0
0032
HR
MIL
0
0031
MN
0
M22
0030
SC
0
S22
0011 _Control
INT
0
0
0010 ^(E2PROM) BL
BP2
BP1
5
0
Y2K21
0
Y21
0
D21
H21
M21
S21
0
BP0
Bit
4
0
Y2K20
0
Y20
G20
D20
H20
M20
S20
0
0
3
0
Y2K13
0
Y13
G13
D13
H13
M13
S13
0
0
2
RWEL
0
DY2
Y12
G12
D12
H12
M12
S12
0
0
Range
1
0 (optional)
WEL
RTCF
0
Y2K10 19/20
DY1
DY0 0-6
Y11
Y10 0-99
G11
G10 1-12
D11
D10 1-31
H11
H10 0-23
M11
M10 0-59
S11
S10 0-59
0
0
00h
0
0
00h
REAL TIME CLOCK REGISTERS
Year 2000 (Y2K)
The X1240 has a century byte that “rolls over” from 19
to 20 when the years byte changes from 99 to 00. The
Y2K byte can contain only the values of 19 or 20.
Day of the Week Register (DW)
This register provides a Day of the Week status and
uses three bits DY2 to DY0 to represent the seven
days of the week. The counter advances in the cycle
0-1-2-3-4-5-6-0-1-2-... The assignment of a numerical
value to a specific day of the week is arbitrary and may
be decided by the system software designer. The
Clock Default values define 0=Sunday.
Clock/Calendar Registers (YR, MO, DT, HR, MN, SC)
These registers depict BCD representations of the
time. As such, SC (Seconds) and MN (Minutes) range
from 00 to 59, HR (Hour) is 1 to 12 with an AM or PM
indicator (H21 bit) or 0 to 23 (with MIL=1), DT (Date) is
1 to 31, MO (Month) is 1 to 12, YR (year) is 0 to 99.
24 Hour Time
If the MIL bit of the HR register is 1, the RTC will use a
24-hour format. If the MIL bit is 0, the RTC will use 12-
hour format and bit H21 will function as an AM/PM
indicator with a ‘1’ representing PM. The clock defaults
to Standard Time with H21=0.
Leap Years
Leap years add the day February 29 and are defined
as those years that are divisible by 4. Years divisible
by 100 are not leap years, unless they are also divisi-
ble by 400. This means that the year 2000 is a leap
year, the year 2100 is not. The X1240 does not correct
for the leap year in the year 2100.
STATUS REGISTER (SR)
The Status Register is located in the RTC area at
address 003FH. This is a volatile register only and is
used to control the WEL and RWEL write enable
latches, and read a Low Voltage Sense bit. This regis-
ter is logically seperated from both the array and the
Clock/Control Registers (CCR).
Table 2. Status Register (SR)
Addr 7 6
003Fh BAT 0
Default 0 0
5 43 2
1
0
0 0 0 RWEL WEL RTCF
0 00 0
0
0
BAT: Battery Supply—Volatile
This bit set to “1” indicates that the device is operating
from V_BACK, not V_CC. It is a read only bit and is set/
reset by hardware.
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