C8051F02X Datasheet, PDF (187/272 Pages) Silicon Laboratories – 8K ISP FLASH MCU Family

C8051F020/1/2/3
18.3. SMBus Transfer Modes
The SMBus0 interface may be configured to operate as a master and/or a slave. At any particular time, the interface
will be operating in one of the following modes: Master Transmitter, Master Receiver, Slave Transmitter, or Slave
Receiver. See Table 18.1 for transfer mode status decoding using the SMB0STA status register. The following mode
descriptions illustrate an interrupt-driven SMBus0 application; SMBus0 may alternatively be operated in polled
mode.
18.3.1. Master Transmitter Mode
Serial data is transmitted on SDA while the serial clock is output on SCL. SMBus0 generates a START condition and
then transmits the first byte containing the address of the target slave device and the data direction bit. In this case the
data direction bit (R/W) will be logic 0 to indicate a "WRITE" operation. The SMBus0 interface transmits one or
more bytes of serial data, waiting for an acknowledge (ACK) from the slave after each byte. To indicate the end of the
serial transfer, SMBus0 generates a STOP condition.
Figure 18.4. Typical Master Transmitter Sequence
S
SLA
WA
Data Byte
A
Data Byte
AP
Interrupt
Interrupt
Interrupt
Interrupt
Received by SMBus
Interface
Transmitted by
SMBus Interface
S = START
P = STOP
A = ACK
W = WRITE
SLA = Slave Address
18.3.2. Master Receiver Mode
Serial data is received on SDA while the serial clock is output on SCL. The SMBus0 interface generates a START
followed by the first data byte containing the address of the target slave and the data direction bit. In this case the data
direction bit (R/W) will be logic 1 to indicate a "READ" operation. The SMBus0 interface receives serial data from
the slave and generates the clock on SCL. After each byte is received, SMBus0 generates an ACK or NACK depend-
ing on the state of the AA bit in register SMB0CN. SMBus0 generates a STOP condition to indicate the end of the
serial transfer.
Figure 18.5. Typical Master Receiver Sequence
S
SLA
RA
Data Byte
A
Data Byte
NP
Interrupt
Interrupt
Received by SMBus
Interface
Transmitted by
SMBus Interface
Interrupt
Interrupt
S = START
P = STOP
A = ACK
N = NACK
R = READ
SLA = Slave Address
Rev. 1.4
187