PCA9550_5

© NXP B.V. 2008. All rights reserved.

Product data sheet

Rev. 05 — 13 October 2008

10 of 26

NXP Semiconductors

PCA9550

7.4 Bus transactions

Fig 11. Write to register

0

A

S

slave address

START condition

R/W

acknowledge

from slave

002aad268

0

0

AI

0

B2B1B0

0

command byte

A

acknowledge

from slave

12345678

SCL

9

SDA

DATA 1

A

write to register

data out from port

acknowledge

from slave

DATA 1 VALID

data to register

10000

A0

1

Fig 12. Read from register

10000

A0

0

A

S1

START condition

R/W

acknowledge

from slave

002aad269

A

acknowledge

from slave

SDA

A

P

acknowledge

from master

data from register

DATA (first byte)

slave address

STOP

condition

S

(repeated)

START condition

(cont.)

(cont.)

1

A

R/W

acknowledge

from slave

slave address

at this moment master-transmitter becomes master-receiver

and slave-receiver becomes slave-transmitter

NA

no acknowledge

from master

data from register

DATA (last byte)

command byte

0

0

AI

0

B2 B1

0B0

Auto-Increment

register address

if AI = 1

10000

A0

1

Remark: This figure assumes the command byte has previously been programmed with 00h.

Fig 13. Read input port register

10000

A0

1

A

S1

START condition

R/W

acknowledge

from slave

002aad270

A

acknowledge

from master

SDA

NA

read from

port

data into

port

P

data from port

no acknowledge

from master

data from port

DATA 4

slave address

DATA 1

STOP

condition

DATA 2

DATA 3

DATA 4

DATA 1