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Product data sheet Rev. 6 — 7 November 2017 13 of 34
NXP Semiconductors
PCA9535; PCA9535C
16-bit I
2
C-bus and SMBus, low power I/O port with interrupt
6.5.2 Reading the port registers
In order to read data from the PCA9535/PCA9535C, the bus master must first send the
PCA9535/PCA9535C address with the least significant bit set to a logic 0 (see Figure 6
“PCA9535; PCA9535C device address”). The command byte is sent after the address and
determines which register will be accessed. After a restart, the device address is sent
again, but this time the least significant bit is set to a logic 1. Data from the register
defined by the command byte will then be sent by the PCA9535/PCA9535C (see
Figure 10
, Figure 11 and Figure 12). Data is clocked into the register on the falling edge of
the acknowledge clock pulse. After the first byte is read, additional bytes may be read but
the data will now reflect the information in the other register in the pair. For example, if you
read Input Port 1, then the next byte read would be Input Port 0. There is no limitation on
the number of data bytes received in one read transmission but the final byte received, the
bus master must not acknowledge the data.
Remark: Transfer can be stopped at any time by a STOP condition.
Fig 10. Read from register
AS
START condition R/W
acknowledge
from slave
002aac222
A
acknowledge
from slave
SDA
A P
acknowledge
from master
DATA (first byte)
slave address
STOP
condition
S
(repeated)
START condition
(cont.)
(cont.)
1 0 0 A2 A1 A0 1 A0
R/W
acknowledge
from slave
slave address
at this moment master-transmitter becomes master-receiver
and slave-receiver becomes slave-transmitter
NA
no acknowledge
from master
COMMAND BYTE
1 0 0 A2 A1 A00 0
data from lower or
upper byte of register
LSBMSB
DATA (last byte)
data from upper or
lower byte of register
LSBMSB
