Atmel Xplained Evaluation Board AT32UC3A3-XPLD AT32UC3A3-XPLD Data Sheet

32072H–AVR32–10/2012

3.

Start the transfer by enabling the Peripheral DMA Controller to receive.

4.

Wait for the Peripheral DMA Controller end-of-receive flag.

5.

Disable the Peripheral DMA Controller.

SMBus mode is enabled by writing a one to the SMBus Mode Enable (SMEN) bit in CR. SMBus
mode operation is similar to I²C operation with the following exceptions:

• Only 7-bit addressing can be used.

• The SMBus standard describes a set of timeout values to ensure progress and throughput on 

the bus. These timeout values must be written to TR.

• Transmissions can optionally include a CRC byte, called Packet Error Check (PEC).

• A dedicated bus line, SMBALERT, allows a slave to get a master’s attention.

• A set of addresses have been reserved for protocol handling, such as Alert Response 

Address (ARA) and Host Header (HH) Address. Address matching on these addresses can 
be enabled by configuring CR appropriately.

Each SMBus transfer can optionally end with a CRC byte, called the PEC byte. Writing a one to
the Packet Error Checking Enable (PECEN) bit in CR enables automatic PEC handling in the
current transfer. The PEC generator is always updated on every bit transmitted or received, so
that PEC handling on following linked transfers will be correct.

In slave receiver mode, the master calculates a PEC value and transmits it to the slave after all
data bytes have been transmitted. Upon reception of this PEC byte, the slave will compare it to
the PEC value it has computed itself. If the values match, the data was received correctly, and
the slave will return an ACK to the master. If the PEC values differ, data was corrupted, and the
slave will return a NAK value. The SR.SMBPECERR bit is set automatically if a PEC error
occurred.

In slave transmitter mode, the slave calculates a PEC value and transmits it to the master after
all data bytes have been transmitted. Upon reception of this PEC byte, the master will compare
it to the PEC value it has computed itself. If the values match, the data was received correctly. If
the PEC values differ, data was corrupted, and the master must take appropriate action.

The PEC byte is automatically inserted in a slave transmitter transmission if PEC enabled when
NBYTES reaches zero. The PEC byte is identified in a slave receiver transmission if PEC
enabled when NBYTES reaches zero. NBYTES must therefore be set to the total number of
data bytes in the transmission, including the PEC byte.

The Timing Register (TR) configures the SMBus timeout values. If a timeout occurs, the slave
will leave the bus. The SR.SMBTOUT bit is also set.

A slave can get the master’s attention by pulling the SMBALERT line low. This is done by writing
a one to the SMBus Alert (SMBALERT) bit in CR. This will also enable address match on the
Alert Response Address (ARA).