Philips Semiconductors

Product data

PCA9558

2002 May 24

11

SW00645

S

100111 A0

0

AA

SLAVE ADDRESS

R/W

ACKNOWLEDGE

FROM SLAVE

ACKNOWLEDGE

FROM SLAVE

COMMAND BYTE

EEPROM ADDRESS

ACKNOWLEDGE

FROM SLAVE

A

a7 a6 a5 a4 a3 a2 a1 a0

P

xxxxxxxx

A

DUMMY BYTE

ACKNOWLEDGE

FROM SLAVE

GPIO INPUT PORT DATA LATCHED

00010010

PROGRAMMING BEGINS AFTER STOP

SEE FIGURE 2 FOR THE NEEDED COMMAND CODE.

Figure 15. Read from GPIO Input Port Register and write to 256 byte EEPROM

RESET

Power-on Reset

the reset condition is released and the PCA9558 registers and

SMBus state machine will initialize to their default states.

External Reset

A reset of the GPIO registers can be accomplished by holding the

I/O_OUT_LOW pin low for a minimum of Tw. These GPIO registers

return to their default states until the I/O_OUT_LOW input is once

again high.

USING THE PCA9558 ON THE SMBus

It is possible to use Intel

® chipsets to communicate with the

PCA9558. There are no limitations when the SMBus Controller is

communicating with the Mux or the GPIO; however, there are

limitations with the 2K serial EEPROM. Because of being able to

address any location in the EEPROM block using the 2nd command

byte, the designer using the PCA9558 on the SMBus will have to

program around it, an easy thing to do. The device designers had to

deal with the specifics of addressing the EEPROM and chose the

the EEPROM block.

In order to write to the EEPROM, write the EEPROM address byte

in the Data0 byte and the data to be sent should be placed in the

Data1 byte. The Intel

® chipset’s Word Data instruction would then

send the address, followed by the command register then Data0

(EEPROM address), and then the Data1 (data byte). A read from

the EEPROM would be a two step process. The first step would be

to do a Write Byte with the EEPROM address in the Data0 register.

The second step would be to do a Receive Byte where the data is

stored in the command register.

Other differences from the SMBus spec:

Paragraph 5.5.5 – Read Byte/Word in figure 5–11 – the

PCA9558 follows this same command code with one exception,

the PCA9558 requires 2 bytes of command before the repeated

start.

Paragraph 5.5.6 – Process call in figure 5–15 – the PCA9558

read operation is very similar to the SMBus process call. In the

PCA9558 read operation you send a start condition – slave

address with a write bit – 2 bytes of command code – repeated

start – slave address with a read bit – then read data.