m41t80 STMicroelectronics, m41t80 Datasheet - Page 7

• Manufacturer Part Number: m41t80
• Description: Serial Access Real Time Clock With Alarm
• Manufacturer: STMicroelectronics

M41T80
2
2.1
2.1.1
2.1.2
2.1.3
Operation
The M41T80 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 20 Bytes
contained in the device can then be accessed sequentially in the following order:
2-Wire bus characteristics
The bus is intended for communication between different IC’s. 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:
Accordingly, the following bus conditions have been defined:
Bus not busy
Both data and clock lines remain High.
Start data transfer
A change in the state of the data line, from high to Low, while the clock is High, defines the
START condition.
Stop data transfer
A change in the state of the data line, from Low to High, while the clock is High, defines the
STOP condition.
1
2
3
4
5
6
7
8
9
10
11
17
20
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.
st
nd
rd
th
th
th
th
th
th
th
th
th
th
Byte: tenths/hundredths of a second register
Byte: century/hours register
Byte: day register
Byte: date register
Byte: month register
Byte: year register
Byte: control register
Byte: minutes register
Byte: seconds register
Byte: 32kE bit
- 16
- 19
Byte: square wave register
th
th
Bytes: alarm registers
Bytes: reserved
Operation
7/25