Datasheet

Product data sheet Rev. 01 — 19 January 2010 4 of 24

NXP Semiconductors

PCA24S08A

1024 × 8-bit CMOS EEPROM with access protection

5.2 Pin description

6. Functional description

Refer to Figure 1 “Block diagram”.

6.1 Device addressing

Following a START condition, the bus master must output the address of the slave it is

accessing. The address of the PCA24S08A is shown in Figure 4

The last bit of the slave address defines the operation to be performed. When set to

logic 1 a read operation is selected, while logic 0 selects a write operation. Bits B2 and B1

in the slave address represent the 2 most significant bits of the word to be addressed. The

third device address bit in the I

C-bus protocol that is usually matched to A2 (pin 3) on a

standard 24C08 serial EEPROM is internally connected HIGH, so device addresses A8h

through AFh (hex) are used to access the memory on the chip.

6.2 Write operations

Write operations on the device can be performed only when WP is held LOW. When the

WP pin is held HIGH, content of the full memory is protected (Block 0 to Block 7,

APP registers, ID Page), and no write operation is allowed.

6.2.1 Byte/word write

Write command may be used to set the address for a subsequent Read command. For a

write operation, the PCA24S08A requires a second address field. The address field

associated with the two software selectable bits in the slave address is a word address

providing access to the 1024 bytes of memory, as shown in Figure 5

. Upon receipt of the

word address, the PCA24S08A responds with an acknowledge and awaits the next 8 bits

of data, again responding with an acknowledge. Word address is automatically

incremented.

Table 2. Pin description

Symbol Pin Description

n.c. 1, 2 not connected

PROT

3 active LOW protect reset input

4 ground supply voltage

SDA 5 serial data; open-drain I/O

SCL 6 serial clock; open-drain input

WP 7 active HIGH write protect input

8 supply voltage

Fig 4. Slave address

002aae78

1 0 1 0 1 B2 B1 R/W

fixed

sofware

selectable