PCA9685 All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2015. All rights reserved.
Product data sheet Rev. 4 — 16 April 2015 28 of 52
NXP Semiconductors
PCA9685
16-channel, 12-bit PWM Fm+ I
2
C-bus LED controller
7.6 Software reset
The Software Reset Call (SWRST Call) allows all the devices in the I
2
C-bus to be reset to
the power-up state value through a specific formatted I
2
C-bus command. To be performed
correctly, it implies that the I
2
C-bus is functional and that there is no device hanging the
bus.
The SWRST Call function is defined as the following:
1. A START command is sent by the I
2
C-bus master.
2. The reserved SWRST I
2
C-bus address ‘0000 000’ with the R/W bit set to ‘0’ (write) is
sent by the I
2
C-bus master.
3. The PCA9685 device(s) acknowledge(s) after seeing the General Call address
‘0000 0000’ (00h) only. If the R/W
bit is set to ‘1’ (read), no acknowledge is returned to
the I
2
C-bus master.
4. Once the General Call address has been sent and acknowledged, the master sends
1 byte with 1 specific value (SWRST data byte 1):
a. Byte 1 = 06h: the PCA9685 acknowledges this value only. If byte 1 is not equal to
06h, the PCA9685 does not acknowledge it.
If more than 1 byte of data is sent, the PCA9685 does not acknowledge any more.
5. Once the correct byte (SWRST data byte 1) has been sent and correctly
acknowledged, the master sends a STOP command to end the SWRST Call: the
PCA9685 then resets to the default value (power-up value) and is ready to be
addressed again within the specified bus free time (t
BUF
).
The I
2
C-bus master must interpret a non-acknowledge from the PCA9685 (at any time) as
a ‘SWRST Call Abort’. The PCA9685 does not initiate a reset of its registers. This
happens only when the format of the SWRST Call sequence is not correct.
Fig 12. SWRST Call
0 0 0 0 0 0 0 AS 0
General Call address
START condition acknowledge
from slave
002aac900
SWRST data byte 1
A
acknowledge
from slave
P
STOP
condition
00001100
