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AC75 AT Command Set

19.8 AT^SSPI

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

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19.8.3 Transmitting 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

AT - Driver

Function in protocol Special

character

Hex value Description

→ 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

(in I²C protocol referred to

as ACK)

+ 0x2B Notifies the AT interface that data were

successfully transmitted or, on the I²C bus,

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.

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