FM3104/16/64/256
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 =
Address
18h
17h
16h
15h
14h
13h
12h
11h
10h
0Fh
0Eh
0Dh
0Ch
0Bh
0Ah
09h
08h
07h
06h
05h
04h
03h
02h
01h
00h
D7
Data
D5
D4
D3
Serial Number Byte 7
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
Counter 2 LSB
Counter 1 MSB
Counter 1 LSB
RC
-
-
WP1
WP0
-
-
WDT4
WDT3
POR
LB
-
WR3
10 years
0
0
10 mo
0
10 date
0
0
0
0
0
10 hours
10 minutes
10 seconds
reserved
CALS
CAL4
CAL3
CF
reserved reserved reserved
D6
D2
D1
D0
Function
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
Watchdog Control
Watchdog Restart/Flags
Years
Month
Date
Day
Hours
Minutes
Seconds
CAL/Control
RTC Control
Range
FFh
FFh
FFh
FFh
FFh
FFh
FFh
FFh
FFh
FFh
FFh
FFh
SNL
WDE
WTR
0
0
0
0
0
0
/OSCEN
reserved
CC
C2P
VBC
VTP1
WDT2
WDT1
WR2
WR1
years
months
date
day
hours
minutes
seconds
CAL2
CAL1
CAL
W
C1P
VTP0
WDT0
WR0
00-99
1-12
1-31
1-7
0-23
0-59
0-59
CAL0
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. 3.2
July 2010
Page 10 of 25
RAMTRON [ RAMTRON INTERNATIONAL CORPORATION ]
