NXP Semiconductors

PCA9849

4-channel ultra-low voltage, Fm+ I2C-bus multiplexer with reset

1. START command

2. The master sends the Reserved Device ID I2C-bus address followed by the R/W bit set to 0 (write): ‘1111

1000’.

3. The master sends the I2C-bus slave address of the slave device it needs to identify. The LSB is a ‘Don’t

care’ value. Only one device must acknowledge this byte (the one that has the I2C-bus slave address).

4. The master sends a Re-START command.

Remark: A STOP command followed by a START command will reset the slave state machine and the

Device ID read cannot be performed. Also, a STOP command or a Re-START command followed by

an access to another slave device will reset the slave state machine and the Device ID Read cannot be

performed.

5. The master sends the Reserved Device ID I2C-bus address followed by the R/W bit set to 1 (read): ‘1111

1001’.

6. The Device ID Read can be done, starting with the 12 manufacturer bits (first byte + 4 MSB of the second

byte), followed by the 9 part identification bits (4 LSBs of the second byte + 5 MSBs of the third byte), and

then the 3 die revision bits (3 LSBs of the third byte).

7. The master ends the reading sequence by NACKing the last byte, thus resetting the slave device state

machine and allowing the master to send the STOP command.

Remark: The reading of the Device ID can be stopped anytime by sending a NACK command.

If the master continues to ACK the bytes after the third byte, the slave rolls back to the first byte and keeps

sending the Device ID sequence until a NACK has been detected.

For the PCA9849, the Device ID is shown in Figure 7.

0

aaa-018028

0

0

1

0

0

0

0

1

0

0

0

0

0

0

0

0

0

0

revision

1

0

0

0

0

part identification

manufacturer

Figure 7. PCA9849 Device ID field

aaa-011781

A7 A6 A5 A4 A3 A2 A1

I2C-bus target address

of the device to be identified

A

no acknowledge

from controller

P

STOP condition

M

11

M

10 M9 M8 M7 M6 M5 M4

Sr

repeated START

condition

1 A

R/W

S 1 1 1 1 1 0 0

Device ID address

START condition

0 A

R/W

acknowledge from

one or several targets

0 A

don't care

acknowledge from

target to be identified

1 1 1 1 1 0 0

Device ID address

acknowledge from

target to be identified

A M3 M2 M1 M0

acknowledge

from controller

manufacturer name = 000000000000

P8 P7 P6 P5 A

acknowledge

from controller

P4 P3 P2 P1 P0 R2 R1 R0

part identification = 100001010

revision = 000

If more than 3 bytes are read, the slave device loops back to the first byte (manufacturer byte) and keeps sending data

until the master generates a ‘no acknowledge’.

Figure 8. Device ID field read operation

PCA9849

All information provided in this document is subject to legal disclaimers.

© 2023 NXP B.V. All rights reserved.

Product data sheet

Rev. 2.0 — 30 June 2023

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