M41ST85W_11 STMICROELECTRONICS [STMicroelectronics], M41ST85W_11 Datasheet - Page 12

• Manufacturer Part Number: M41ST85W_11
• Description: 3.0/3.3 V I2C combination serial RTC, NVRAM supervisor and microprocessor supervisor
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

Operating modes
2
2.1
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Operating modes
The M41ST85W clock operates as a slave device on the serial bus. Access is obtained by
implementing a start condition followed by the correct slave address (D0h). The 64 bytes
contained in the device can then be accessed sequentially in the following order:
1.
2.
3.
4.
5.
6.
7.
8.
9.
10. Watchdog register
11 - 16. Alarm registers
17 - 19. Reserved
20. Square wave register
21 - 64. User RAM
The M41ST85W clock continually monitors V
V
address counter. Inputs to the device will not be recognized at this time to prevent erroneous
data from being written to the device from a an out-of-tolerance system. When V
below V
ultralow current mode of operation to conserve battery life. As system power returns and
V
external V
Write protection continues until V
For more information on battery storage life refer to application note AN1012.
2-wire bus characteristics
The bus is intended for communication between different ICs. It consists of two lines: a bi-
directional data signal (SDA) and a clock signal (SCL). Both the SDA and SCL lines must be
connected to a positive supply voltage via a pull-up resistor.
The following protocol has been defined:
●
●
●
CC
CC
fall below V
rises above V
Tenths/hundredths of a second register
Seconds register
Minutes register
Century/hours register
Day register
Date register
Month register
Year register
Control register
Data transfer may be initiated only when the bus is not busy.
During data transfer, the data line must remain stable whenever the clock line is high.
Changes in the data line, while the clock line is high, will be interpreted as control
signals.
SO
CC
, the device automatically switches over to the battery and powers down into an
.
PFD
SO
, the device terminates an access in progress and resets the device
, the battery is disconnected, and the power supply is switched to
Doc ID 7531 Rev 11
CC
reaches V
CC
PFD
for an out-of-tolerance condition. Should
(min) plus t
rec
(min).
M41ST85W
CC
falls