PCA9675
NXP Semiconductors
Remote 16-bit I/O expander for Fm+ I2C-bus with interrupt
7.2.1 Software Reset
The Software Reset Call allows all the devices in the I2C-bus to be reset to the power-up
state value through a specific formatted I2C-bus command. To be performed correctly, it
implies that the I2C-bus is functional and that there is no device hanging the bus.
The Software Reset sequence is defined as following:
1. A START command is sent by the I2C-bus master.
2. The reserved General Call I2C-bus address ‘0000 000’ with the R/W bit set to 0 (write)
is sent by the I2C-bus master.
3. The PCA9675 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 I2C-bus master.
4. Once the General Call address has been sent and acknowledged, the master sends
1 byte. The value of the byte must be equal to 06h.
a. The PCA9675 acknowledges this value only. If the byte is not equal to 06h, the
PCA9675 does not acknowledge it.
If more than 1 byte of data is sent, the PCA9675 does not acknowledge any more.
5. Once the right byte has been sent and correctly acknowledged, the master sends a
STOP command to end the Software Reset sequence: the PCA9675 then resets to
the default value (power-up value) and is ready to be addressed again within the
specified bus free time. If the master sends a Repeated START instead, no reset is
performed.
The I2C-bus master must interpret a non-acknowledge from the PCA9675 (at any time) as
a ‘Software Reset Abort’. The PCA9675 does not initiate a reset of its registers.
The unique sequence that initiates a Software Reset is described in Figure 10.
2
SWRST Call I C address
SWRST data = 06h
S
0
0
0
0
0
0
0
0
A
0
0
0
0
0
1
1
0
A
P
START condition
R/W
acknowledge
from slave(s)
acknowledge
from slave(s)
PCA9675 is(are) reset.
Registers are set to default power-up values.
002aac156
Fig 10. Software Reset sequence
PCA9675
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© NXP B.V. 2011. All rights reserved.
Product data sheet
Rev. 2 — 3 October 2011
9 of 34
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