PCA9671 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2011. All rights reserved.
Product data sheet Rev. 3 — 29 September 2011 9 of 33
NXP Semiconductors
PCA9671
Remote 16-bit I/O expander for Fm+ I
2
C-bus with reset
7.2.1 Software Reset
The Software Reset 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 Software Reset sequence is defined as following:
1. A START command is sent by the I
2
C-bus master.
2. The reserved General Call I
2
C-bus address ‘0000 000’ with the R/W bit set to logic 0
(write) is sent by the I
2
C-bus master.
3. The PCA9671 device(s) acknowledge(s) after seeing the General Call address
‘0000 0000’ (00h) only. If the R/W
bit is set to logic 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. The value of the byte must be equal to 06h.
a. The PCA9671 acknowledges this value only. If the byte is not equal to 06h, the
PCA9671 does not acknowledge it.
If more than 1 byte of data is sent, the PCA9671 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 PCA9671 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 I
2
C-bus master must interpret a non-acknowledge from the PCA9671 (at any time) as
a ‘Software Reset Abort’. The PCA9671 does not initiate a reset of its registers.
The unique sequence that initiates a Software Reset is described in Figure 10
.
Fig 10. Software Reset sequence
002aac281
0 0 0 0 0 0 0 AS 0
SWRST Call I
2
C-bus address
START condition R/W
acknowledge
from slave(s)
0 0 0 0 1 1 00
SWRST data = 06h
A
acknowledge
from slave(s)
P
PCA9671 is(are) reset.
Registers are set to default power-up values.
