Datasheet
PCA9541A All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2014. All rights reserved.
Product data sheet Rev. 5 — 24 April 2014 12 of 45
NXP Semiconductors
PCA9541A
2-to-1 I
2
C-bus master selector with interrupt logic and reset
[1] BUSON and NBUSON is an exclusive-OR type function where:
Equal values (00b or 11b) means that the connection between the upstream and the downstream channels
is off.
Different values (01b or 10b) means that the connection between the upstream and the downstream
channels is on.
Switch to the new channel is done when the master initiating the switch request sends a
STOP command to the PCA9541A.
If either master wants to change the connection of the downstream channel, it must write
to its Control Register (Reg#01), and then send a STOP command because an update
of the connection to the downstream according to the values in the two internal Control
Registers happens only on a STOP command. Writing to one control register followed by
a STOP condition on the other master's channel does not cause an update to the
downstream connection.
When both masters request a switch to their own channel at the same time, the master
who last wrote to its Control Register before the PCA9541A receives a STOP command
wins the switching sequence. There is no arbitration performed.
The Auto Increment feature (AI = 1) allows programming the PCA9541A in 4 bytes:
Start
111A3A2A1A0 + 0 PCA9541 Address + Write
00010000 Select Reg#00 with AI = 1
Data Reg#00 Interrupt Enable Register data
Data Reg#01 Control Register data
Stop
Table 12 describes which command must be written to the Control Register when a
master device wants to take control of the I
2
C-bus. Byte written to the Control Register is
a function of the current I
2
C-bus control status performed after an initial reading of the
Control Register.
Table 10. BUSON and NBUSON truth table
NBUSON
[1]
BUSON
[1]
Slave channel
00off
10on
01on
11off
Table 11. Default Control Register values
Type version Master Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
NTESTON TESTON not used BUSINIT NBUSON BUSON NMYBUS MYBUS
PCA9541A/01MST_000000100
MST_100001010
PCA9541A/03MST_000000000
MST_100000010