C8051F321-GMR Datasheet, PDF (172/250 Pages) Silicon Laboratories – Full Speed USB, 16 k ISP FLASH MCU Family

C8051F320/1
16.3.4. 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 10 SMBus clock source periods. If the SMBus is waiting to generate a
Master START, the START will be generated following this timeout. Note that a clock source is required for
free timeout detection, even in a slave-only implementation.
16.4. Using the SMBus
The SMBus can operate in both Master and Slave modes. The interface provides timing and shifting con-
trol for serial transfers; higher level protocol is determined by user software. The SMBus interface provides
the following application-independent features:
• Byte-wise serial data transfers
• Clock signal generation on SCL (Master Mode only) and SDA data synchronization
• Timeout/bus error recognition, as defined by the SMB0CF configuration register
• START/STOP timing, detection, and generation
• Bus arbitration
• Interrupt generation
• Status information
SMBus interrupts are generated for each data byte or slave address that is transferred. When transmitting,
this interrupt is generated after the ACK cycle so that software may read the received ACK value; when
receiving data, this interrupt is generated before the ACK cycle so that software may define the outgoing
ACK value. See Section “16.5. SMBus Transfer Modes” on page 180 for more details on transmission
sequences.
Interrupts are also generated to indicate the beginning of a transfer when a master (START generated), or
the end of a transfer when a slave (STOP detected). Software should read the SMB0CN (SMBus Control
register) to find the cause of the SMBus interrupt. The SMB0CN register is described in Section
“16.4.2. SMB0CN Control Register” on page 176; Table 16.4 provides a quick SMB0CN decoding refer-
ence.
SMBus configuration options include:
• Timeout detection (SCL Low Timeout and/or Bus Free Timeout)
• SDA setup and hold time extensions
• Slave event enable/disable
• Clock source selection
These options are selected in the SMB0CF register, as described in Section “16.4.1. SMBus Configuration
Register” on page 173.
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