PCA9501_4

© NXP B.V. 2009. All rights reserved.

Product data sheet

Rev. 04 — 10 February 2009

8 of 28

NXP Semiconductors

PCA9501

7.4 Memory operations

7.4.1 Write operations

Write operations require an additional address field to indicate the memory address

location to be written. The address field is eight bits long providing access to any one of

the 256 words of memory. There are two types of write operations, ‘byte write’ and ‘page

write’.

Write operation is possible when the Write Control pin (WC) is put at a LOW logic level (0).

When this control signal is set at 1, write operation is not possible and data in the memory

is protected.

‘Byte write’ and ‘page write’ explained below assume that WC is set to 0.

7.4.1.1

Byte write

To perform a byte write, the START condition is followed by the memory slave address and

the R/W bit set to 0. The PCA9501 will respond with an acknowledge and then consider

the next eight bits sent as the word address and the eight bits after the word address as

the data. The PCA9501 will issue an acknowledge after the receipt of both the word

address and the data. To terminate the data transfer the master issues the STOP

condition, initiating the internal write cycle to the non-volatile memory. Only write and read

operations to the quasi-bidirectional I/Os are allowed during the internal write cycle.

Fig 10. Application of multiple PCA9501s with interrupt

Fig 11. Interrupt generated by a change of input to IO5

002aad293

MICROCONTROLLER

INT

PCA9501

INT

PCA9501

INT

device 1

device 2

PCA9501

INT

device 16

1

A

S

slave address (I/O expander)

START condition

R/W

acknowledge

from slave

002aad294

1

data from port

1

12345678

SCL

9

SDA

data into IO5

INT

A5 A4 A3 A2 A1 A0

0

IO5

P

STOP

condition