M41T256YMH7F View Datasheet(PDF) -

M41T256Y

2

Operating modes

Operating modes

The M41T256Y 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 256K bytes

contained in the device can then be accessed sequentially in the following order:

0-7FEF = General purpose RAM

7FF0-7FF6 = Reserved

7FF7h = Tenths/hundredths register

7FF8h = Control register

7FF9h = Seconds register

7FFAh = Minutes register

7FFBh = Hour register

7FFCh = Tamper/day register

7FFDh = Date register

7FFEh = Month register

7FFFh = Year register

The M41T256Y clock continually monitors VCC for an out-of tolerance condition. Should

VCC fall below VPFD, the device terminates an access in progress and resets the device

address counter. Inputs to the device will not be recognized at this time to prevent

erroneous data from being written to the device from an out-of-tolerance system. When VCC

falls below VSO, the device automatically switches over to the battery and powers down into

an ultra low current mode of operation to conserve battery life. As system power returns and

VCC rises above VSO, the battery is disconnected, and the power supply is switched to

external VCC. Write protection continues until VCC reaches VPFD plus tREC.

For more information on Battery Storage Life refer to Application Note AN1012.

2.1

2.1.1

2-wire bus characteristics

The bus is intended for communication between different ICs. It consists of two lines: a

bidirectional 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:

● 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.

Accordingly, the following bus conditions have been defined:

Bus not busy

Both data and clock lines remain High.

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