Datasheet

PCA9670 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
Product data sheet Rev. 3 — 30 May 2013 12 of 35
NXP Semiconductors
PCA9670
Remote 8-bit I/O expander for Fm+ I
2
C-bus with reset
8.2 Writing to the port (Output mode)
The master (microcontroller) sends the START condition and slave address, setting the
last bit of the address byte to logic 0 for the write mode. The PCA9670 acknowledges and
the master then sends the data byte for P7 to P0 to the port register. As the clock line
goes HIGH, the 8-bit data is presented on the port lines after it has been acknowledged by
the PCA9670. If a LOW is written, the strong pull-down turns on and stays on. If a HIGH is
written, the strong pull-up turns on for
1
⁄
2
of the clock cycle, then the line is held HIGH by
the weak current source. The master can then send a STOP condition or continuing
sending data. The number of data bytes that can be sent successively is not limited and
the previous data is overwritten every time a data byte has been sent and acknowledged.
Ensure a logic 1 is written for any port that is being used as an input to ensure the strong
external pull-down is turned off.
Fig 12. Simple quasi-bidirectional I/O
002aah683
V
DD
weak 100 µA
current source
(inactive when
output LOW)
output HIGH
V
SS
output LOW
accelerator
pull-up
P port
P7 - P0
pull-down with
resistor to V
SS
or
external drive LOW
input LOW
pull-up with
resistor to V
DD
or
external drive HIGH
input HIGH
Fig 13. Write mode (output)
A5 A4 A3 A2 A1 A0 0 ASA6
slave address
START condition R/W
acknowledge
from slave
002aac265
P6 1P7
data 1
A
acknowledge
from slave
12345678SCL 9
SDA
A
acknowledge
from slave
write to port
data output from port
t
v(Q)
P5
data 2
DATA 2 VALID
P4 P3 P2 P1 P0 P7 P4 P3 P2 P1 P00
P5
P5
t
v(Q)
DATA 1 VALID
P5 output voltage
I
trt(pu)
I
OH
P5 pull-up output current