Datasheet

PCA9570 All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2014. All rights reserved.
Product data sheet Rev. 4 — 17 September 2014 8 of 32
NXP Semiconductors
PCA9570
Remote 4-bit general purpose outputs for 1 MHz I
2
C-bus
8. I/O programming
8.1 I/O architecture
The device ports (see Figure 2) are entirely independent and are output ports. The state
of the ports at the pin is transferred from the ports to the microcontroller in the Read mode
(see Figure 13
). Output data is transmitted to the ports in the Write mode (see Figure 12).
At power-on all ports are HIGH. The state of the Output Port register determines if either
Q1 or Q2 is on, driving the line either HIGH or LOW. A bit set to 1 in the data byte drives
the line HIGH at the corresponding port. A bit set to 0 in the data byte drives the line LOW
at the corresponding port.
If an external voltage is applied to an output, care should be exercised because of the
low-impedance path that exists between the pin and either V
DD
or V
SS
.
8.2 Writing to the port (Output mode)
To write, the master (microcontroller) first addresses the slave device. By setting the last
bit of the byte containing the slave address to logic 0, the Write mode is entered. The
device acknowledges and the master sends the data byte for P7 to P0 and is
acknowledged by the device. Writes to P7 to P4 are ignored in the PCA9570 as only P3
through P0 are available. The 4-bit data is presented on the port lines after it has been
acknowledged by the device. The number of data bytes that can be sent successively is
not limited. The previous data is overwritten every time a data byte has been sent.
If more than 3 bytes are read, the slave device loops back to the first byte (manufacturer byte) and keeps sending data until the
master generates a ‘no acknowledge’.
Fig 11. Device ID field reading
002aah310
A6 A5 A4 A3 A2 A1 A0
I
2
C-bus slave address
of the device to be identified
A
no acknowledge
from master
P
STOP condition
M
11
M
10
M9 M8 M7 M6 M5 M4
Sr
repeated START
condition
1 A
R/W
S 1 1 1 1 1 0 0
Device ID address
START condition
0 A
R/W
acknowledge from
one or several slaves
x A
don’t care
acknowledge from
slave to be identified
1 1 1 1 1 0 0
Device ID address
acknowledge from
slave to be identified
A M3 M2 M1 M0
acknowledge
from master
manufacturer name = 000000000000
P8 P7 P6 P5 A
acknowledge
from master
P4 P3 P2 P1 P0 R2 R1 R0
part identification = 100000000 revision = 000