CP2400 Ver la hoja de datos (PDF) - Silicon Laboratories
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CP2400 Datasheet PDF : 110 Pages
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CP2400/1/2/3
15.3.3. SCL Low Timeout
If the SCL line is held low by a slave device on the bus, no further communication is possible. Furthermore, the
master cannot force the SCL line high to correct the error condition. To solve this problem, the SMBus protocol
specifies that devices participating in a transfer must detect any clock cycle held low longer than 25 ms as a
“timeout” condition. Devices that have detected the timeout condition must reset the communication no later than
10 ms after detecting the timeout condition.
When SMBus is used for communication with the host microcontroller, Timer 0 is used to detect SCL low timeouts.
Timer 0 is forced to reload when SCL is high, and allowed to count when SCL is low. With Timer 0 enabled and
configured to overflow after 25 ms, the Timer 0 interrupt service routine can be used to alert the host
microcontroller of an SCL Low Timeout. After an SCL Low Timeout, the SMBus slave will reset its internal state
machine and will be ready to respond to new transfers. On reset or wake-up from ULP mode, Timer 0 is enabled
and configured for SCL Low Timeout detection. The SCL Low Timeout may be disabled by clearing the SMBTOE
bit in the SMB0CF register. This allows full software control of Timer 0.
15.3.4. SCL High (SMBus Free) Timeout
The SMBus specification stipulates that if the SCL and SDA lines remain high for more that 50 µs, the bus is
designated as free. When the SMBFTE bit in SMB0CF is set, the bus will be considered free if SCL and SDA
remain high for more than 1250 system clock periods. After an SCL High Timeout, the SMBus slave will reset its
internal state machine and will be ready to respond to new transfers.
15.3.5. Slave Address Selection
CP2400/1/2/3 devices can have one of 2 possible 7-bit, left-justified slave addresses: 0x74 and 0x76. The least
significant bit of the slave address is set by the SMBA0 pin. The remaining bits in the slave address are fixed. The
bit following the least significant address bit is used to indicate whether the current transfer is a read or a write.
106
Rev. 1.0
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