Comtrol AT Commands - Manual (Page 159)

AT Commands for CX81801/CX06833/CX81300/CX06827 Modems Reference Manual
102184B Conexant 4-5
as the end of stream marker, and is not transmitted. All data received from the DTE after
the <DLE><ETX> is ignored by the modem until the modem generates either the
CONNECT, OK, or ERROR result code.
If no more data is in the transmit buffer, and the last transmitted character was not an
ASCII NULL, the modem generates the OK result code and returns to the command
mode. If the last character transmitted was an ASCII NULL, the modem generates the
CONNECT message to the DTE and waits for further data from the DTE while
transmitting NULLs to the remote. If more data is received before five seconds elapse,
the modem continues to transmit the data as described in the previous paragraph. If five
seconds elapse and no data is received from the DTE, the modem drops carrier, goes on-
hook, and generates the ERROR result code.
4.1.9 Fax Data Reception
Fax data reception is initiated using the AT+FRM=<mod> command. After this
command is issued, the modem looks for carrier in the modulation scheme specified by
the parameter n. If no carrier is detected before the period of time specified by register S7
expires, the modem generates the NO CARRIER message and returns to command mode.
If a V.21 carrier is detected when a high speed carrier is expected, the modem generates
the +FCERROR message and returns to the command mode. If the specified carrier is
detected, the modem generates the CONNECT message and enters the data receive mode.
While in data receive mode, the modem receives data from the remote, adds start and
stop bits, and handles <DLE><chr> character pairs before passing the data to the DTE.
The modem prefixes each <DLE> character with another <DLE> character before
sending it to the DTE.
If the modem detects a receive buffer overflow condition, it stops receiving from the
remote until there is room in the receive buffer. The modem informs the DTE of the
buffer overflow after it sends to the DTE the last character that was stored in the buffer
before the overflow occurred.
If the modem receives any character from the DTE after the +FRM command (except
flow control characters if software flow control is in effect), or if the modem detects a
high-to-low transition of the DTR signal while &D1 is in effect, it sends <DLE><ETX>
to the DTE, generates the OK result code, and returns to command mode. The receive
buffer is cleared and all data received from the remote is discarded. If loss of DTR is
detected while &D2 is in effect, the modem goes on-hook, sends <DLE><ETX>
followed by OK result code to the DTE, and returns to command mode. If the modem
detects a DTR drop while &D3 is in effect, the modem performs a warm reset.