8 Channel Capacitive Touch Sensor with 2 LED Drivers
Datasheet
Chapter 3 Communications
3.1
Communications
The CAP1128 communicates using the 2-wire SMBus or I2C bus, the 2-wire proprietary BC-Link, or
the SPI bus. Regardless of communication mechanism, the device functionality remains unchanged.
The communications mechanism as well as the SMBus (or I2C) slave address is determined by the
resistor connected between the ADDR_COMM pin and ground as shown in Table 3.1.
Table 3.1 ADDR_COMM Pin Decode
PULL-DOWN RESISTOR (+/- 5%)
PROTOCOL USED
SMBUS ADDRESS
SPI Communications using
Normal 4-wire Protocol Used
GND
56k
n/a
SPI Communications using Bi-
Directional 3-wire Protocol Used
n/a
68k
82k
BC-Link Communications
SMBus / I2C
n/a
0101_100(r/w)
0101_011(r/w)
0101_010(r/w)
0101_001(r/w)
0101_000(r/w)
100k
120k
150k
VDD
SMBus / I2C
SMBus / I2C
SMBus / I2C
SMBus / I2C
2
3.1.1
SMBus (I C) Communications
When configured to communicate via the SMBus, the CAP1128 supports the following protocols: Send
Byte, Receive Byte, Read Byte, Write Byte, Read Block, and Write Block. In addition, the device
supports I2C formatting for block read and block write protocols.
APPLICATION NOTE: For SMBus/I2C communications, the SPI_CS# pin is not used and should be grounded; any
data presented to this pin will be ignored.
See Section 3.2 and Section 3.3 for more information on the SMBus bus and protocols respectively.
3.1.2
3.1.3
SPI Communications
When configured to communicate via the SPI bus, the CAP1128 supports both bi-directional 3-wire
and normal 4-wire protocols and uses the SPI_CS# pin to enable communications.
See Section 3.5 and Section 3.6 for more information on the SPI bus and protocols respectively.
BC-Link Communications
When BC-Link communications are used, the CAP1128 supports the read byte protocol and the write
byte protocol.
APPLICATION NOTE: For BC-Link communications, the SPI_CS# pin is not used and should be grounded; any
data presented to this pin will be ignored.
SMSC CAP1128
Revision 1.32 (01-05-12)
DATA1S7HEET
SMSC [ SMSC CORPORATION ]
