SAM4L Datasheet, PDF (714/1185 Pages) ATMEL Corporation – ATSAM ARM-based Flash MCU

ATSAM4L4/L2
1. Write CMDR with TENBIT=1, REPSAME=0, READ=0, START=1, STOP=0,
NBYTES=0 and the desired address.
2. Write NCMDR with TENBIT=1, REPSAME=1, READ=1, START=1, STOP=1 and the
desired address and NBYTES value.
Figure 27-15. A Read Transfer with 10-bit Addressing
1 1 1 1 0XX0
S
SLAVE ADDRESS
1st 7 bits
RW A1
SLAVE ADDRESS
2nd byte
1 1 1 1 0XX1
A2 Sr
SLAVE ADDRESS
1st 7 bits
RW A3 DATA A
DATA A P
27.8.9
SMBus Mode
SMBus mode is enabled and disabled by writing to the SMEN and SMDIS bits 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 into SMBTR.
• Transmissions can optionally include a CRC byte, called Packet Error Check (PEC).
• A set of addresses have been reserved for protocol handling, such as Alert Response
Address (ARA) and Host Header (HH) Address.
27.8.9.1
Packet Error Checking
Each SMBus transfer can optionally end with a CRC byte, called the PEC byte. Writing a one to
CMDR.PECEN enables automatic PEC handling in the current transfer. Transfers with and with-
out PEC can freely be intermixed in the same system, since some slaves may not support PEC.
The PEC LFSR is always updated on every bit transmitted or received, so that PEC handling on
combined transfers will be correct.
In master transmitter 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 NACK value. The DNAK bit in SR reflects the state of the last received
ACK/NACK value. Some slaves may not be able to check the received PEC in time to return a
NACK if an error occurred. In this case, the slave should always return an ACK after the PEC
byte, and some other mechanism must be implemented to verify that the transmission was
received correctly.
In master receiver 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 SR.PECERR is set. In master receiver mode, the
PEC byte is always followed by a NACK transmitted by the master, since it is the last byte in the
transfer.
The PEC byte is automatically inserted in a master transmitter transmission if PEC is enabled
when NBYTES reaches zero. The PEC byte is identified in a master receiver transmission if
PEC is enabled when NBYTES reaches zero. NBYTES must therefore be written with the total
number of data bytes in the transmission, including the PEC byte.
42023C–SAM–02/2013
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