Silicon Laboratories C8051F343 Manuel D’Utilisation

Serial data is received 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 direc-
tion bit. In this case the data direction bit (R/W) will be logic 1 (READ). Serial data is then received from the 
slave on SDA while the SMBus outputs the serial clock. The slave transmits one or more bytes of serial 
data. After each byte is received, ACKRQ is set to ‘1’ and an interrupt is generated. Software must write 
the ACK bit (SMB0CN.1) to define the outgoing acknowledge value (Note: writing a ‘1’ to the ACK bit gen-
erates an ACK; writing a ‘0’ generates a NACK). Software should write a ‘0’ to the ACK bit after the last 
byte is received, to transmit a NACK. The interface exits Master Receiver Mode after the STO bit is set and 
a STOP is generated. Note that the interface will switch to Master Transmitter Mode if SMB0DAT is written 
while an active Master Receiver. Figure 17.6 shows a typical Master Receiver sequence. Two received 
data bytes are shown, though any number of bytes may be received. Notice that the ‘data byte transferred’ 
interrupts occur 

before the ACK cycle in this mode.

Data Byte

Data Byte

A

N

A

S

R

P

SLA

S = START
P = STOP
A = ACK
N = NACK
R = READ
SLA = Slave Address

Received by SMBus
Interface

Transmitted by
SMBus Interface

Interrupt

Interrupt

Interrupt

Interrupt