M41T94 datasheet(13/41 Pages) STMICROELECTRONICS

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M41T94

Operation

13/41

3.1

SPI bus characteristics

The Serial Peripheral interface (SPI) bus is intended for synchronous communication

between different ICs. It consists of four signal lines: Serial data input (SDI), Serial data

output (SDO), Serial clock (SCL) and a Chip Enable (E).

By definition a device that gives out a message is called “transmitter,” the receiving device

that gets the message is called “receiver.” The device that controls the message is called

“master.” The devices that are controlled by the master are called “slaves.”

The E input is used to initiate and terminate a data transfer. The SCL input is used to

synchronize data transfer between the master (micro) and the slave (M41T94) devices.

The SCL input, which is generated by the microcontroller, is active only during address and

data transfer to any device on the SPI bus (see Figure 5 on page 9).

The M41T94 can be driven by a microcontroller with its SPI peripheral running in either of

the two following modes:

●

(CPOL, CPHA) = ('0', '0') or

●

(CPOL, CPHA) = ('1', '1').

For these two modes, input data (SDI) is latched in by the low-to-high transition of clock

SCL, and output data (SDO) is shifted out on the high-to-low transition of SCL (see Table 2

on page 10 and Figure 6 on page 10).

There is one clock for each bit transferred. Address and data bits are transferred in groups

of eight bits. Due to memory size the second most significant address bit is a Don’t Care

(address bit 6).

Figure 7.

Input timing requirements

AI04633

SCL

SDI

MSB IN

SDO

tDVCH

HIGH IMPEDANCE

LSB IN

tELCH

tCHDX

tDLDH

tDHDL

tCHCL

tCLCH

tEHCH

tEHEL

tCHEH

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