PCA9674 datasheet(11/34 Pages) PHILIPS

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PCA9674_PCA9674A_2

Product data sheet

Rev. 02 — 12 October 2006

11 of 34

NXP Semiconductors

PCA9674/74A

Remote 8-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 PCA9674/74A 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 PCA9674/74A acknowledges this value only. If the byte is not equal to 06h, the

PCA9674/74A does not acknowledge it.

If more than 1 byte of data is sent, the PCA9674/74A 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 PCA9674/74A 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 PCA9674/74A (at any

time) as a ‘Software Reset Abort’. The PCA9674/74A does not initiate a reset of its

registers.

The unique sequence that initiates a Software Reset is described in Figure 11.

Fig 10. Device ID address

R/W

002aac116

Fig 11. Software Reset sequence

002aac262

SWRST Call I2C-bus address

START condition

R/W

acknowledge

from slave(s)

SWRST data = 06h

acknowledge

from slave(s)

PCA9674/74A is(are) reset.

Registers are set to default power-up values.

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