Philips Semiconductors

Product data

PCA24S08

1024

× 8-bit CMOS EEPROM with access protection

2004 May 10

9

ACCESS PROTECTION PAGE

The serial port may be used to read and write the Access Protection

Page (APP) and ID Page using device access codes B8h and B9h

instead of the normal value of A8h through AFh (hex) that are used

to access the rest of the EEPROM memory. The second byte of

write commands (the word address) should be in the range of 00h

through 0Fh for the APP page and 10h through 1Fh for the ID page.

This coding is shown in the Access Protection Page Examples

section.

Reads and writes to these two pages may take place on a single

byte basis only. Multi-byte operations will be NACK’ed.

As an example, the bit encoding for a single byte read and write

command are shown in the Access Protection Page Examples

section.

The PCA24S08 will acknowledge all device addresses of B8h or

B9h. If the most significant three its of the word address are not all 0

(indicating an address outside the Access protection and ID pages),

the chip will NACK the access.

Bytes 0 through 7 of the APP contain 8 identical set of access

control fields (PBx and SBx) for each of the eight blocks of memory

on the chip, which operate according to the table listed in the

Access Protection section above. When the sticky bit in one of these

bytes is set, that byte can be written by the system. Once a sticky bit

is reset (written to zero) by the software, the byte containing it can

no longer be modified by the software until the next power cycle.

These bytes can always be read by the system.

controls read and write access to the last 7 bytes (9–15) of the APP

and all 16 bytes of the ID page according to the encoding listed in

HIGH. This byte can always be read by the system. Bit 0 through 6

of this byte are stored in EEPROM memory and do not change

when the power is cycled or the PROT pin changes state.

Byte 9 contains the 8 block 0 write protection bits (WPN) for each

page within block 0.

Byte 10 emulates a coil detection feature to keep compatibility with

existing software controlling device.

Even though the PCA24S08 does not have the RFID capability of

the AT24RF03C, it gives a “coil non detected” information when the

detection feature is initiated.

The detection feature uses the Detection Enable bit (DE) and the

Detect Coil bit (DC). At power-up, DE = 0 and DC = 1. Detection is

enabled by setting DE bit at 1. Since no coil is detected, DC is then

automatically reset and equal to 0.

DE is a Read/Write bit, DC is a Read Only bit. Attempt to write to

this bit will be ignored.

Bit 0 in the same byte emulates a Tamper bit and is always equal

to 0.

TAMPER is a Read Only bit. Attempt to write a ‘1’ to this bit will be

ignored.

Bytes 11 through 14 are currently reserved and should not be used

by the system. Byte 14 may not be written by the device at any time.

Byte 11 to 13 are read/write bytes that are stored in the EEPROM.

Byte 14 is a read only byte and the returned value during a read

operation is FFh. A write on it is acknowledged but the write will be

ignored.

Device Access Examples

For Write Operations:

1 0 1 1 1 0 0 0

For Read Operations:

Byte 15 contains device revision information stored in the EEPROM.

It is set at the wafer production facility and cannot be changed in the

field, so any write to this byte will be ignored but acknowledged. The

value of this byte is 10h.

The memory map for the access protection page is shown in the

APP Memory Map table. In this table, an X means that the value is a

don’t care upon writing and that it is undefined upon reading. The

PB fields are all two bits wide, and the Device Revision field is 8 bits

wide. All other fields are on bit wide.

With the exception of the 9 sticky bits (SB) the two coil detect bits

(DE and DC), the tamper bit (TAMPER) and bytes 14 and 15, all bits

within the Access Protection Page are stored in EEPROM memory.

Their state does not change if power is removed or when the PROT

pin is held LOW.

ID field that would be transmitted by the device from the RFID port.

Bytes within it are accessed with the address byte at B8h or B9h

(write/read). Reading and writing to this page is permitted when