FM32L278/L276/L274/L272 - 3V I2C Companion
Register Map
The processor companion functions are accessed via 16 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
00-08h
D7
D6
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
FC
WP1
WP0
-
WDT4
WDT3
LB
-
WR3
DO NOT USE
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
RESERVED
Range
FFh
FFh
FFh
FFh
FFh
FFh
FFh
FFh
FFh
FFh
FFh
FFh
SNL
WDE
WTR
-
-
POR
CC
VBC
WDT2
WR2
C2P
-
WDT1
WR1
C1P
VTP
WDT0
WR0
*Note that the usable address range starts at address 09h to preserve software compatibility with the FM31L27x
device family, which includes a real-time clock in registers 00-08h.
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
Hex Value
0x00
0x00
0x00
0x00
0x00
0x00
0x00
0x00
0x00
0x1F
Rev. 3.0
Feb. 2009
Page 7 of 21
RAMTRON [ RAMTRON INTERNATIONAL CORPORATION ]
