Siemens AC75 manual Transmitting Data over AT Interface, Channel Open / Close

AC75 AT Command Set

19.8 AT^SSPI

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19.8.3Transmitting Data over AT Interface

This section provides information on the protocol used for data transmission to or from I²C/SPI devices and explains the data mode. It is assumed that you are familiar with the I²C specification.

Throughout this section the following document conventions are used to mark the direction of send and receive: Transfer Message: AT → I²C or SPI device driver

Response Message: AT ← I²C or SPI device driver

Channel Open / Close:

To change from command mode to data mode use the AT^SSPI write command. To close down the channel and return to command mode send the ASCII code # (0x23).

ASCII Protocol for I²C or SPI communication over AT interface:

The protocol allows using a Terminal program for the communication between the module and the I²C slave device/SPI device. To visualize transferred characters and response data it is recommended to run the Terminal program in chat mode or to switch on local echo.

For transfer and response, special characters are defined, such as Start and Stop to mark a single message and Close to disconnect the data channel. All valid special characters are listed below:

Table 19.3: Special characters for ASCII coding
Direction	Function in protocol	Special	Hex value	Description
AT - Driver		character
→	Start Transfer Message	<	0x3C	Special character sent to the I²C/SPI
				driver to start sending.
→	Stop Transfer Message	>	0x3E	Special character sent to the I²C/SPI
				driver to stop sending.
→	Channel Close	#	0x23	For signalling.
				Channel Close can be sent any time inside
				or outside a transmit or receive message.
				Causes the transfer to be aborted and
				takes the ME back to AT command mode.
←	Start Response Message	{	0x7B	Special character sent to the I²C/SPI
				driver to mark the beginning of a Response
				Message.
←	Stop Response Message	}	0x7D	Special character sent to the I²C/SPI
				driver to mark the end of a Response Mes-
				sage.
←	Protocol error	!	0x21	For signalling.
				Reports to the AT interface that the Trans-
				fer Frame does not comply with the proto-
				col definition (syntax error).
←	Transmission OK	+	0x2B	Notifies the AT interface that data were
	(in I²C protocol referred to			successfully transmitted or, on the I²C bus,
	as ACK)			the I²C Slave Address was recognized.

On I²C bus only:

←

Transmission error

(in I²C protocol referred to as NAK)

-

0x2D

Notifies the AT interface that data transmis- sion failed or the I²C Slave Address was not recognized. On the I²C bus, the faulty data byte (16 bit byte counter) is identified as well.

AC75_ATC_V01.002	Page 500 of 569	10/30/06
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