STTS2004 datasheet(36/58 Pages) STMICROELECTRONICS

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SPD EEPROM operation

STTS2004

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DocID024229 Rev 3

5.5.1

Byte write

After the device select code and the address byte, the bus master sends one data byte. If

the addressed location is hardware write-protected, the device replies to the data byte with

NoAck, and the location is not modified. If, instead, the addressed location is not write-

protected, the device replies with Ack. The bus master terminates the transfer by generating

a Stop condition, as shown in Figure 13.

Figure 13. Write mode sequences in a non write-protected area

5.5.2

Page write

The Page write mode allows up to 16 bytes to be written in a single Write cycle, provided

that they are all located in the same page in the memory: that is, the most significant

memory address bits are the same. If more bytes are sent than will fit up to the end of the

page, a condition known as ‘roll-over’ occurs. This should be avoided, as data starts to

become overwritten in an implementation dependent way.

The bus master sends from 1 to 16 bytes of data, each of which is acknowledged by the

device if Write Control (WC) is low. If the addressed location is hardware write-protected,

the device replies to the data byte with NoAck, and the locations are not modified. After

each byte is transferred, the internal byte address counter (the 4 least significant address

bits only) is incremented. The transfer is terminated by the bus master generating a Stop

condition.

5.5.3

Minimizing system delays by polling on ACK

The sequence, as shown in Figure 14, is:



Initial condition: a Write cycle is in progress.



Step 1: the bus master issues a Start condition followed by a device select code (the

first byte of the new instruction).



Step 2: if the device is busy with the internal Write cycle, no Ack will be returned and

the bus master goes back to Step 1. If the device has terminated the internal Write

cycle, it responds with an Ack, indicating that the device is ready to receive the second

part of the instruction (the first byte of this instruction having been sent during Step 1).

Byte Write

Device select

Byte address

Data in

Page Write

Device select

Byte address

Data in 1

Data in 2

AI01941b

Data in N

ACK

R/W

ACK

R/W

ACK

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