Datasheet

V
CC
V
POR
V
PORF
Time
POR
Time
PCA9539
www.ti.com SCPS130F –AUGUST 2005–REVISED JANUARY 2011
Figure 21. V
POR
Interrupt Requirements
The expected performance of the interrupt feature is that INT is to be cleared (de-asserted) when the input
register is read or all inputs return to the last read values. INT is also de-asserted when both of the following
occur:
• The last I
2
C command byte (register pointer) written was 00h. This generally means the last operation with
the device was a read of the input register, but the command byte may have been written with 00h without
ever going on to read the Input register.
• Any other slave device on the I
2
C bus acknowledges an address byte with the R/W bit set high. This occurs
when reading any other valid device on the bus.
In order to prevent INT from de-asserting when another device is read on the I
2
C bus, the user needs to change
the command byte to something other than 00 (hex) after a read operation to the device.
RESET Requirements
For proper operation of the RESET feature, it is essential that the RESET pin is at the same or lower voltage
than the V
CC
pin. If RESET is at a higher voltage than V
CC
, current drains from the RESET pin into V
CC
and pulls
V
CC
above its voltage level.
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