Smartwatch comparison register definition, Figure 1, Nonvolatile controller operation – Rainbow Electronics DS1216 User Manual
Page 4: Freshness seal
DS1216
4 of 13
SMARTWATCH COMPARISON REGISTER DEFINITION
Figure 1
Note:
The pattern recognition in Hex is C5, 3A, 5C, C5, 3A, A3, 5C. The odds of this pattern
accidentally duplicating and causing inadvertent entry to the SmartWatch are less than 1 in 10
19
. This
pattern is sent to the SmartWatch LSB to MSB.
After power-up, the controller could be in the 64-bit clock register read/write sequence (from an
incomplete access prior to power-down). Therefore, it is recommended that a 64-bit read be performed
upon power-up to prevent accidental writes to the clock, and to prevent reading clock data when access to
the RAM would otherwise be expected.
NONVOLATILE CONTROLLER OPERATION
The DS1216 SmartWatch performs circuit functions required to make a CMOS RAM nonvolatile. First, a
switch is provided to direct power from the battery or V
CC
supply, depending on which voltage is greater.
This switch has a voltage drop of less than 0.2V. The second function that the SmartWatch provides is
power-fail detection, which occurs at V
TP
. The DS1216 constantly monitors the V
CC
supply. When V
CC
goes out of tolerance, a comparator outputs a power-fail signal to the chip-enable logic. The third function
accomplishes write protection by holding the chip-enable signal to the memory within 0.2V of V
CC
or
battery. During nominal power-supply conditions, the memory chip-enable signal will track the chip-
enable signal sent to the socket with a maximum propagation delay of 7ns for the 5V and 12ns for the
3.3V version.
FRESHNESS SEAL
Each DS1216 is shipped from Dallas Semiconductor with its lithium energy source disconnected,
ensuring full energy capacity. When V
CC
is first applied at a level greater than the lithium energy source
is enabled for battery-backup operation.
1
1
0
0
0
1
0
1
0
0
1
1
1
0
1
0
1
0
1
0
0
0
1
1
0
1
0
1
1
1
0
0
1
1
0
0
0
1
0
1
0
0
1
1
1
0
1
0
1
0
1
0
0
0
1
1
0
1
0
1
1
1
0
0
BYTE 0
BYTE 1
BYTE 2
BYTE 3
BYTE 4
BYTE 5
BYTE 6
BYTE 7
C5
3A
A3
5C
C5
3A
A3
5C
HEX
VALUE
7
0