FM3204/16/64/256
Rev 2.1
Dec. 2004
Page 7 of 20
be tied to 5V since the VBAK (max) specification
will be exceeded. A 1 µF capacitor will keep
the companion functions working for about 1.5
second.
Although VBAK may be connected to VSS, this is not
recommended if the companion is used. None of the
companion functions will operate below about 2.5V.
!
!
!
! Note: systems using lithium batteries should clear
the VBC bit to 0 to prevent battery charging. The
VBAK circuitry includes an internal 1 K
Ω series
resistor as a safety element.
Register Map
The processor companion functions are accessed via 16 special function registers that are mapped to a separate 2-
wire device ID. The interface protocol is described below. The registers contain control bits, or information flags. A
description of each register follows.
Register Map Summary Table
Nonvolatile =
Battery-backed =
Data
Address
D7
D6
D5
D4
D3
D2
D1
D0
Function
Range
Serial Number Byte 7
Serial Number 7
FFh
Serial Number Byte 6
Serial Number 6
FFh
Serial Number Byte 5
Serial Number 5
FFh
Serial Number Byte 4
Serial Number 4
FFh
Serial Number Byte 3
Serial Number 3
FFh
Serial Number Byte 2
Serial Number 2
FFh
Serial Number Byte 1
Serial Number 1
FFh
Serial Number Byte 0
Serial Number 0
FFh
10h
Counter 2 MSB
Event Counter 2 MSB
FFh
0Fh
Counter 2 LSB
Event Counter 2 LSB
FFh
0Eh
Counter 1 MSB
Event Counter 1 MSB
FFh
0Dh
Counter 1 LSB
Event Counter 1 LSB
FFh
0Ch
-
-
-
-
RC
CC
C2P
C1P
Event Count Control
0Bh
SNL
-
-
WP1
WP0
VBC
VTP1
VTP0
Companion Control
0Ah
WDE
-
-
WDT4
WDT3
WDT2
WDT1
WDT0
Watchdog Control
09h
WTR
POR
LB
-
WR3
WR2
WR1
WR0
Watchdog Restart/Flags
00-08h
RESERVED
DO NOT USE
18h
17h
11h
16h
15h
14h
13h
12h
*Note that the usable address range starts at address 09h to preserve software compatibility with the FM31xx
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
Hex Value
18h
0x00
17h
0x00
16h
0x00
15h
0x00
14h
0x00
13h
0x00
12h
0x00
11h
0x00
0Bh
0x00
0Ah
0x1F
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