STTS2002 datasheet(33/52 Pages) STMICROELECTRONICS

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STTS2002

SPD EEPROM operation

Doc ID 15389 Rev 5

33/52

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 23). 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 (A1 and A2, as shown in

Table 23).

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. Also, once the PSWP instruction has been

successfully executed, the STTS2002 SPD no longer acknowledges any instruction (with a

device type identifier of 0110) to access the write-protection settings.

Figure 11.

Setting the write protection

Reading write-protection status

The status of software write protection can be determined using these instructions:

●

Read SWP: Read Write Protection status

●

Read PSWP: Read Permanently Set Write Protection status

Read SWP

The controller issues a Read SWP command. If Software Write Protection has not been set,

the device replies to the data byte with an Ack. If Software Write Protection has been set,

the device replies to the data byte with a NoAck.

Read PSWP

The controller issues a Read PSWP command. If Permanent Software Write Protection has

not been set, the device replies to the data byte with an Ack. If Permanent Software Write

Protection has been set, the device replies to the data byte with a NoAck.

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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