Silicon Laboratories SI2493/57/34/15/04 manual Response, Dleetxcrlfno Carriercrlf, Connect 1CRLF

AN93

After the host receives “CONNECT “, it sends the frame data followed by <DLE><ETX>. A frame includes type, length, payload and checksum. The frame data can contain anything, including <DLE><ETX>. No DLE shielding is needed. <DLE><ETX> with no data for about 8ms is treated as the end of frame.

After a frame has been sent, the modem response will be: <CR><LF>OK<CR><LF>

On the answer modem side, the command AT+FRM=200 causes the receiver to look for at least 32 bits of CS and for at least 60 bits of marks. The answer modem detects the protocol of the transaction by whether CS comes before the marks.

AT+FRM=200	Receive an SMS frame
AT:UD2,<RxTimeout>	Set RxTimeout:

There can be several responses to AT+FRM=200, depending on the received data.

9.2.2.2. Response 1

If the frame had not been received within the time specified in RxTimeout, the modem response to the host would be:

<DLE><ETX><CR><LF>NO CARRIER<CR><LF>

9.2.2.3. Response 2

If the frame had been received with a mark segment at beginning of frame, the modem would respond to the host with:

CONNECT 1<CR><LF>

<Frame Data Received><DLE><ETX> <CR><LF>OK <CR><LF>

No frame checking would be done by the modem; all of that would be left to the host. As shown above, <DLE><ETX> marks the end of frame. After sending OK to the host, the modem goes back into command mode.

9.2.2.4. Response 3

If the frame had been received with channel seizure and mark segment detected at beginning of frame, the modem would send one of the responses below to the host:

CONNECT 2<CR><LF>

<Frame Data Received><DLE><ETX> <CR><LF>OK <CR><LF>

The Host does all upper level frame validations, since the modem does not do any frame checking. As shown above, <DLE><ETX> signifies the end of frame. After the modem sends OK, it goes back to command mode.

238 Rev. 1.3