STTS424E02 datasheet(31/51 Pages) STMICROELECTRONICS

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STTS424E02

SPD EEPROM operation

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5.4.1

SWP and CWP

If the software write-protection has been set with the SWP instruction, it can be cleared

again with a CWP instruction.

The two instructions (SWP and CWP) have the same format as a Byte Write instruction, but

with a different Device Type Identifier (as shown in Table 20). Like the Byte Write instruction,

it is followed by an address byte and a data byte, but in this case the contents are all “Don’t

Care” (Figure 11). Another difference is that the voltage, VHV, must be applied on the A0 pin,

and specific logical levels must be applied on the other two address pins A1 and A2 (as

shown in Table 20).

5.4.2

PSWP

If the software write-protection has been set with the PSWP instruction, the first 128 bytes of

the memory are permanently write-protected. This write-protection cannot be cleared by

any instruction, or by power-cycling the device, and regardless the state of Write Control

(WC). Also, once the PSWP instruction has been successfully executed, the SPD EEPROM

no longer acknowledges any instruction (with a Device Type Identifier of 0110) to access the

write-protection settings.

Figure 11.

Setting the write protection (WC = 0)

5.5

Write operations

Following a Start condition the bus master sends a Device Select Code with the RW bit

reset to 0. The device acknowledges this, as shown in Figure 12, and waits for an address

byte. The device responds to the address byte with an acknowledge bit, and then waits for

the data byte.

When the bus master generates a Stop condition immediately after the Ack bit (in the “10th

bit” time slot), either at the end of a Byte Write or a Page Write, the internal memory Write

cycle is triggered. A Stop condition at any other time slot does not trigger the internal Write

cycle.

During the internal Write cycle, Serial Data (SDA) and Serial Clock (SCL) are ignored, and

the device does not respond to any requests.

SDA LINE

AI01935B

ACK

WORD

ADDRESS

VALUE

(DON'T CARE)

ACK

DATA

VALUE

(DON'T CARE)

ACK

CONTROL

BYTE

BUS ACTIVITY

MASTER

BUS ACTIVITY

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