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TC63_ATC_V00.490

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5/24/05

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Each Message consists of a Start and Stop character, a Message-ID, further protocol data and user data. The

notation of all elements is explained below: 

Notation of Message-ID:
• All ASCII characters between 0x00...0x7F. It is recommended to use only the characters 0...9, A...Z, a...z.
• Length of the Message-ID: only one character
Notation of protocol data (except Message-ID) and user data:
• Hex (0...9, a...f, A...F)
• Without "0x" (0x01 

→01)

• Each hex value consists of 2 characters (1 

→01)

• Without delimiters such as comma, semicolon, space etc. (0xAE 0x01 0xA5 

→AE01A5)

• In a Transfer Message, the number of the I²C Slave Address and all subsequent written user data shall be

even. If it is odd, a protocol error will be reported. (Keep in mind that the number of all characters transmitted

between Start "<" and Stop ">" of the Transfer Frame shall always be odd because the ID is one character

only.) 

• Length of I²C Slave Address and user data: 

≤ 2048 bytes

The first element of each message is the Start character ("<" for Transfer, "{" for the Response). Accordingly, the

last character of a message is the Stop character (">" for Transfer, "}" for the Response). 

The second element of each message is the Message ID (1 character). The Message ID serves the user to dis-

tinguish between different messages. It is only relevant on protocol level (between AT interface and I²C device

driver), i.e. it is not sent to the I²C slave device. 

Each transfer to the device is followed by a Response Message sent from the driver to the AT interface. The

response includes the Message ID and either OK ("+") or error characters ("-" or "!"). A successful response to

a Read Message contains the OK character and the read data. If an error occurs on the I²C bus, the response

consists of an error character followed by a 16 bit code specifying the faulty byte. 

After each Transfer Message, wait for the Response Message before sending the next Transfer Message. 

All characters entered outside a valid message (i.e. not input between Start character "<" and Stop character ">")

are ignored. 

Table 19.4:  Structure of Transfer and Response Messages on the I²C bus

On the I²C bus, read and write data are handled in two separate frames transmitted one after the other. This is

because the I²C bus has only two bus lines, I2CDAT for the serial data and I2CCLK for the serial clock. Write

data are packed into a Transfer Frame. Read data are packed into a Response Frame. The Transfer Frame con-

tains a Receive or Transmit Request (R/W Request) for the I²C master. 

Frame

Format

Write Transfer Message

< ID SlaveAddress Data >

Maximum length: 2048 bytes for I²C Slave Address 

and written data. LSB of I²C Slave Address = "0".

Read Transfer Message

< ID SlaveAddress ReadLength >

Read Length 

≤ 2048 bytes. LSB I²C of Slave Address 

= "1".

Response Message

      Write OK

      Read of x bytes OK

      NAK for x

th

 byte if Read or Write

      Protocol error in x

th

 byte 

{ID + }

{ID + Data }

{ID - xxxx }

{ID ! xxxx }