C8051F310 datasheet(153/224 Pages) ETC1

153 / 224 page

Rev. 1.6

153

C8051F310/1/2/3/4/5/6/7

14.5. SMBus Transfer Modes

The SMBus interface may be configured to operate as master and/or slave. At any particular time, it will be

operating in one of the following four modes: Master Transmitter, Master Receiver, Slave Transmitter, or

Slave Receiver. The SMBus interface enters Master Mode any time a START is generated, and remains in

Master Mode until it loses an arbitration or generates a STOP. An SMBus interrupt is generated at the end

of all SMBus byte frames; however, note that the interrupt is generated before the ACK cycle when operat-

ing as a receiver, and after the ACK cycle when operating as a transmitter.

14.5.1. Master Transmitter Mode

Serial data is transmitted on SDA while the serial clock is output on SCL. The SMBus interface generates

the START condition and transmits the first 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 0 (WRITE). The master then transmits

one or more bytes of serial data. After each byte is transmitted, an acknowledge bit is generated by the

slave. The transfer is ended when the STO bit is set and a STOP is generated. Note that the interface will

switch to Master Receiver Mode if SMB0DAT is not written following a Master Transmitter interrupt.

Figure 14.5 shows a typical Master Transmitter sequence. Two transmit data bytes are shown, though any

number of bytes may be transmitted. Notice that the ‘data byte transferred’ interrupts occur after the ACK

cycle in this mode.

Figure 14.5. Typical Master Transmitter Sequence

Data Byte

SLA

S = START

P = STOP

A = ACK

W = WRITE

SLA = Slave Address

Received by SMBus

Interface

Transmitted by

SMBus Interface

Interrupt

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