CAP1296 Datasheet, PDF (12/68 Pages) Microchip Technology – 6-Channel Capacitive Touch Sensor with Proximity

CAP1296
3.2.6 SMBUS TIMEOUT
The CAP1296 includes an SMBus timeout feature. Following a 30ms period of inactivity on the SMBus where the
SMCLK pin is held low, the device will timeout and reset the SMBus interface.
The timeout function defaults to disabled. It can be enabled by setting the TIMEOUT bit in the Configuration register
(see Section 5.6, "Configuration Registers").
3.2.7
SMBUS AND I²C COMPATIBILITY
The major differences between SMBus and I²C devices are highlighted here. For more information, refer to the SMBus
2.0 specification.
1. CAP1296supports I²C fast mode at 400kHz. This covers the SMBus max time of 100kHz.
2. Minimum frequency for SMBus communications is 10kHz.
3. The SMBus client protocol will reset if the clock is held low longer than 30ms (timeout condition). This can be
enabled in the CAP1296 by setting the TIMEOUT bit in the Configuration register. I²C does not have a timeout.
4. The SMBus client protocol will reset if both the clock and the data line are high for longer than 200us (idle con-
dition). This can be enabled in the CAP1296by setting the TIMEOUT bit in the Configuration register. I²C does
not have an idle condition.
5. I²C devices do not support the Alert Response Address functionality (which is optional for SMBus).
6. I²C devices support block read and write differently. I²C protocol allows for unlimited number of bytes to be sent
in either direction. The SMBus protocol requires that an additional data byte indicating number of bytes to read /
write is transmitted. The CAP1296 supports I²C formatting only.
3.3 SMBus Protocols
The CAP1296 is SMBus 2.0 compatible and supports Write Byte, Read Byte, Send Byte, and Receive Byte as valid
protocols as shown below.
All of the below protocols use the convention in Table 3-1.
TABLE 3-1: PROTOCOL FORMAT
Data Sent to
Device
Data sent
Data Sent to the
HOst
Data sent
3.3.1 SMBUS WRITE BYTE
The Write Byte is used to write one byte of data to a specific register as shown in Table 3-2.
TABLE 3-2: WRITE BYTE PROTOCOL
Start
Slave
Address
WR
ACK
1 ->0
0101_000
0
0
Register
Address
XXh
ACK
0
Register
Data
XXh
ACK
0
Stop
0 -> 1
3.3.2 SMBUS READ BYTE
The Read Byte protocol is used to read one byte of data from the registers as shown in Table 3-3.
DS00001569B-page 12
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