PCA9570DP datasheet(6/32 Pages) NXP

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PCA9570

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Product data sheet

Rev. 4 — 17 September 2014

6 of 32

NXP Semiconductors

PCA9570

Remote 4-bit general purpose outputs for 1 MHz I2C-bus

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 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 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 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 I2C-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

SWRST Call I2C-bus address

START condition

R/W

acknowledge

from slave(s)

SWRST data = 06h

acknowledge

from slave(s)

PCA9570/PCA9571 is(are) reset.

Registers are set to default power-up values.

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