Datasheet

PCA9570 All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2014. All rights reserved.
Product data sheet Rev. 4 — 17 September 2014 6 of 32
NXP Semiconductors
PCA9570
Remote 4-bit general purpose outputs for 1 MHz I
2
C-bus
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 0 (write)
is sent by the I
2
C-bus master.
3. The device acknowledges 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. The value of the byte must be equal to 06h.
a. The device acknowledges this value only. If the byte is not equal to 06h, the device
does not acknowledge it.
If more than 1 byte of data is sent, the device 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 device 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 device (at any time) as a
‘Software Reset Abort’. The device does not initiate a reset of its registers.
The unique sequence that initiates a Software Reset is described in Figure 9
.
Fig 9. Software Reset sequence
002aag882
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
PCA9570/PCA9571 is(are) reset.
Registers are set to default power-up values.