Datasheet
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
0101XX1AS 1
START condition
R/W
acknowledge
from slave
DATA P
STOP condition
A
no acknowledge
from master
DATA
auto-increment
word address
last byte
002aae79
4
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