PCA24S08A_1

© NXP B.V. 2010. All rights reserved.

Product data sheet

Rev. 01 — 19 January 2010

8 of 24

NXP Semiconductors

PCA24S08A

1024

× 8-bit CMOS EEPROM with access protection

6.4 Access protection

Write operation on the Access protection registers can be performed when WP pin is

LOW. If the WP pin is HIGH, all write operations are prohibited from the serial port,

although write commands may be used to set the address for a subsequent read

command.

All access protection bits are stored on a separate page of the EEPROM that is not

accessed using the normal commands of a PCA24S08A memory. See Section 6.4.2.2

“Access Protection Page (APP)” for more detail on this information.

6.4.1 RFID access fields (RF)

Even though the PCA24S08A does not have the RFID capability, RFID access fields (RF)

can be stored in order to keep existing software compatibility. The fields are stored in the

EEPROM and organized as shown in Table 3.

6.4.2 Protection bits (PB)

The protection bits fields in the Access Protection Page determine what type of accesses

will be permitted via the serial port for each of the blocks on the chip. If an illegal access is

attempted, the command will be NACKed. The MSB (if clear) prohibits all access to the

block, and the LSB (if clear) prohibits writes. The fields are stored in the EEPROM and are

organized as shown in Table 4.

Fig 9.

Master read PCA24S08A immediately after first byte (read mode); current address read

0101

X

X

1

A

S

1

START condition

R/W

acknowledge

from slave

DATA

P

STOP condition

A

no acknowledge

from master

DATA

auto-increment

word address

last byte

002aae794

n bytes

A

auto-increment

word address

acknowledge

from master

Table 3.

RFID access field organization

MSB

LSB

Function

0

0

no accesses permitted from RFID port

0

1

no accesses permitted from RFID port

1

0

read only from RFID port

1

1

no restrictions for RFID accesses

Table 4.

PB organization

MSB

LSB

Function

0

0

no accesses permitted in the block

0

1

no accesses permitted in the block

1

0

read only; writes cause a NACK

1

1

read/write; no access constraints for data within this block