PCA9539_PCA9539R
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Product data sheet
Rev. 6 — 6 February 2013
14 of 37
NXP Semiconductors
PCA9539; PCA9539R
16-bit I2C-bus and SMBus low power I/O port with interrupt and reset
6.6.3 Interrupt output
The open-drain interrupt output is activated when one of the port pins changes state and
the pin is configured as an input. The interrupt is deactivated when the input returns to its
previous state or the Input port register is read (see
Figure 10). A pin configured as an
output cannot cause an interrupt. Since each 8-bit port is read independently, the interrupt
caused by Port 0 will not be cleared by a read of Port 1 or the other way around.
Remark: Changing an I/O from an output to an input may cause a false interrupt to occur
if the state of the pin does not match the contents of the Input port register.
7.
Characteristics of the I2C-bus
The I2C-bus is for 2-way, 2-line communication between different ICs or modules. The two
lines are a serial data line (SDA) and a serial clock line (SCL). Both lines must be
connected to a positive supply via a pull-up resistor when connected to the output stages
of a device. Data transfer may be initiated only when the bus is not busy.
7.1 Bit transfer
One data bit is transferred during each clock pulse. The data on the SDA line must remain
stable during the HIGH period of the clock pulse as changes in the data line at this time
will be interpreted as control signals (see
Figure 12).
7.1.1 START and STOP conditions
Both data and clock lines remain HIGH when the bus is not busy. A HIGH-to-LOW
transition of the data line while the clock is HIGH is defined as the START condition (S). A
LOW-to-HIGH transition of the data line while the clock is HIGH is defined as the STOP
Fig 12. Bit transfer
mba607
data line
stable;
data valid
change
of data
allowed
SDA
SCL
Fig 13. Definition of START and STOP conditions
mba608
SDA
SCL
P
STOP condition
S
START condition