PCA9535E, PCA9535EC
http://onsemi.com
10
Registers 4 and 5: Polarity Inversion Registers
These registers allow the polarity of the data in the input
port registers to be inverted. The input port data polarity will
be inverted when its corresponding bit in these registers is
set (written with ‘1’), and retained when the bit is cleared
(written with a ‘0’).
Table 12. POLARITY INVERSION PORT 0 REGISTER
Bit 7 6 5 4 3 2 1 0
Symbol N0.7 N0.6 N0.5 N0.4 N0.3 N0.2 N0.1 N0.0
Default 00000000
Table 13. POLARITY INVERSION PORT 1 REGISTER
Bit 7 6 5 4 3 2 1 0
Symbol N1.7 N1.6 N1.5 N1.4 N1.3 N1.2 N1.1 N1.0
Default 00000000
Registers 6 and 7: Configuration Registers
The I/O pin directions are configured through the
configuration registers. When a bit in the configuration
registers is set (written with ‘1’), the bit’s corresponding port
pin is enabled as an input with the output driver in
high−impedance. When a bit is cleared (written with ‘0’),
the corresponding port pin is enabled as an output. At reset,
the device’s ports are inputs.
Table 14. CONFIGURATION PORT 0 REGISTER
Bit 7 6 5 4 3 2 1 0
Symbol C0.7 C0.6 C0.5 C0.4 C0.3 C0.2 C0.1 C0.0
Default 11111111
Table 15. CONFIGURATION PORT 1 REGISTER
Bit 7 6 5 4 3 2 1 0
Symbol C1.7 C1.6 C1.5 C1.4 C1.3 C1.2 C1.1 C1.0
Default 11111111
Power−on Reset
Upon application of power, an internal Power−On Reset
(POR) holds the PCA9535E/PCA9535EC in a reset
condition while VDD is ramping up. When VDD has reached
VPOR, the reset condition is released and the
PCA9535E/PCA9535EC registers and SMBus state
machine will initialize to their default states. The reset is
typically completed by the POR and the part enabled by the
time the power supply is above VPOR. However, when doing
a power reset cycle, it is necessary to lower the power supply
below 0.2 V, and then restored to the operating voltage.
I/O Port (See Figure 2)
When an I/O pin is configured as an input on the
PCA9535E, FETs Q1 and Q2 are off, creating a
high−impedance input. The input voltage may be raised
above VDD to a maximum of 5.5 V. In the case of
PCA9535EC, FET Q1 has been removed and the
open−drain FET Q2 will function the same as PCA9535E.
When the I/O pin is configured as an output on the
PCA9535E, then either Q1 or Q2 is enabled, depending on
the state of the output port register. With the PCA9535EC,
an external pullup is required to pull the I/O pin HIGH when
its corresponding output port register bit is a 1. Care should
be exercised if an external voltage is applied to an I/O
configured as an output because of the low−impedance path
that exists between the pin and either VDD or VSS.