NXP Semiconductors
PCA9634
8-bit Fm+ I 2 C-bus LED driver
7.5 Power-on reset
When power is applied to V DD , an internal power-on reset holds the PCA9634 in a reset
condition until V DD has reached V POR . At this point, the reset condition is released and the
PCA9634 registers and I 2 C-bus state machine are initialized to their default states (all
zeroes) causing all the channels to be deselected. Thereafter, V DD must be lowered below
0.2 V to reset the device.
7.6 Software Reset
The Software Reset Call (SWRST Call) allows all the devices in the I 2 C-bus to be reset to
the power-up state value through a speci?c 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 SWRST Call function is de?ned as the following:
1. A START command is sent by the I 2 C-bus master.
2. The reserved SWRST I 2 C-bus address ‘0000 011’ with the R/W bit set to ‘0’ (write) is
sent by the I 2 C-bus master.
3. The PCA9634 device(s) acknowledge(s) after seeing the SWRST Call address
‘0000 0110’ (06h) 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 SWRST Call address has been sent and acknowledged, the master sends
2 bytes with 2 speci?c values (SWRST data byte 1 and byte 2):
a. Byte 1 = A5h: the PCA9634 acknowledges this value only. If byte 1 is not equal to
A5h, the PCA9634 does not acknowledge it.
b. Byte 2 = 5Ah: the PCA9634 acknowledges this value only. If byte 2 is not equal to
5Ah, then the PCA9634 does not acknowledge it.
If more than 2 bytes of data are sent, the PCA9634 does not acknowledge any more.
5. Once the right 2 bytes (SWRST data byte 1 and byte 2 only) have been sent and
correctly acknowledged, the master sends a STOP command to end the SWRST Call:
the PCA9634 then resets to the default value (power-up value) and is ready to be
addressed again within the speci?ed bus free time (t BUF ).
The I 2 C-bus master must interpret a non-acknowledge from the PCA9634 (at any time) as
a ‘SWRST Call Abort’. The PCA9634 does not initiate a reset of its registers. This
happens only when the format of the SWRST Call sequence is not correct.
PCA9634_6
? NXP B.V. 2008. All rights reserved.
Product data sheet
Rev. 06 — 12 September 2008
16 of 38
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