FM31L278/L276/L274/L272 - 3V I2C Companion
Register Map
The RTC and processor companion functions are accessed via 25 special function registers mapped to a separate 2-
wire device ID. The interface protocol is described below. The registers contain timekeeping data, control bits, or
information flags. A description of each register follows the summary table below.
Register Map Summary Table
Nonvolatile =
Battery-backed =
D7
D6
D5
D4
D3
D2
D1
D0
Function
Range
FFh
FFh
FFh
FFh
FFh
FFh
FFh
FFh
FFh
FFh
FFh
FFh
Address
18h
17h
16h
15h
14h
13h
12h
11h
Serial Number Byte 7
Serial Number 7
Serial Number 6
Serial Number 5
Serial Number 4
Serial Number 3
Serial Number 2
Serial Number 1
Serial Number 0
Event Counter 2 MSB
Event Counter 2 LSB
Event Counter 1 MSB
Event Counter 1 LSB
Event Count Control
Companion Control
Serial Number Byte 6
Serial Number Byte 5
Serial Number Byte 4
Serial Number Byte 3
Serial Number Byte 2
Serial Number Byte 1
Serial Number Byte 0
Counter 2 MSB
10h
0Fh
0Eh
0Dh
0Ch
0Bh
0Ah
09h
08h
07h
06h
05h
04h
03h
02h
01h
00h
Counter 2 LSB
Counter 1 MSB
Counter 1 LSB
RC
CC
VBC
WDT2
WR2
C2P
-
WDT1
WR1
C1P
VTP
SNL
WDE
WTR
-
-
FC
-
LB
WP1
WDT4
-
WP0
WDT3
WR3
WDT0 Watchdog Control
WR0 Watchdog Restart/Flags
POR
Years
Month
Date
00-99
1-12
1-31
1-7
0-23
0-59
0-59
10 years
years
months
date
0
0
0
0
0
0
0
0
0
0
0
0
10 mo
10 date
0
0
Day
day
Hours
Minutes
Seconds
10 hours
hours
minutes
seconds
10 minutes
10 seconds
CALS
/OSCEN reserved
reserved CF
CAL4
CAL3
CAL2
CAL
CAL1
W
CAL0 CAL/Control
RTC Control
reserved reserved reserved
R
Note: When the device is first powered up and programmed, all registers must be written because the battery-
backed register values cannot be guaranteed. The table below shows the default values of the non-volatile
registers. All other register values should be treated as unknown.
Default Register Values
Address
18h
17h
16h
15h
14h
13h
12h
11h
0Bh
0Ah
01h
Hex Value
0x00
0x00
0x00
0x00
0x00
0x00
0x00
0x00
0x00
0x1F
0x80
Rev. 3.0
Feb. 2009
Page 10 of 25
RAMTRON [ RAMTRON INTERNATIONAL CORPORATION ]
