Slave Transmitter Mode; Smbus Status Decoding; Figure 15.8. Typical Slave Transmitter Sequence - Silicon Laboratories C8051F330 Manual

C8051F330/1/2/3/4/5

15.5.4. Slave Transmitter Mode

Serial data is transmitted on SDA and the clock is received on SCL. When slave events are enabled (INH
= 0), the interface enters Slave Receiver Mode (to receive the slave address) when a START followed by a
slave address and direction bit (READ in this case) is received. Upon entering Slave Transmitter Mode, an
interrupt is generated and the ACKRQ bit is set. Software responds to the received slave address with an
ACK, or ignores the received slave address with a NACK. If the received slave address is ignored, slave
interrupts will be inhibited until a START is detected. If the received slave address is acknowledged, data
should be written to SMB0DAT to be transmitted. The interface enters Slave Transmitter Mode, and trans-
mits one or more bytes of data. After each byte is transmitted, the master sends an acknowledge bit; if the
acknowledge bit is an ACK, SMB0DAT should be written with the next data byte. If the acknowledge bit is
a NACK, SMB0DAT should not be written to before SI is cleared (Note: an error condition may be gener-
ated if SMB0DAT is written following a received NACK while in Slave Transmitter Mode). The interface
exits Slave Transmitter Mode after receiving a STOP. Note that the interface will switch to Slave Receiver
Mode if SMB0DAT is not written following a Slave Transmitter interrupt. Figure 15.8 shows a typical Slave
Transmitter sequence. Two transmitted data bytes are shown, though any number of bytes may be trans-
mitted. Notice that the 'data byte transferred' interrupts occur after the ACK cycle in this mode.
S SLA
Received by SMBus
Interface
Transmitted by
SMBus Interface

Figure 15.8. Typical Slave Transmitter Sequence

15.6. SMBus Status Decoding

The current SMBus status can be easily decoded using the SMB0CN register. In the table below, STATUS
VECTOR refers to the four upper bits of SMB0CN: MASTER, TXMODE, STA, and STO. The shown
response options are only the typical responses; application-specific procedures are allowed as long as
they conform to the SMBus specification. Highlighted responses are allowed but do not conform to the
SMBus specification.
150
R A Data Byte A
Interrupt Interrupt
Rev. 1.7
Interrupt
Data Byte N P
Interrupt
S = START
P = STOP
N = NACK
R = READ
SLA = Slave Address