Fax Data Reception - AOpen FM56 Manual

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.