Rockwell RCV144ACx, Command Reference Manual, Page: 105 / 186

AT Command Reference Manual
1048 5-3
<DLE><ETX>, generates the ERROR message, and returns to command mode. The modem keeps looking for HDLC flags
followed by more data from the remote, with the selected modulation scheme.
If the modem detects a receive buffer overflow condition, it concludes that there was an FCS error in that frame. The modem
will receive more frames only if a starting flag is detected and there is room in the receive buffer. If a starting flag is detected
and there is no room in the buffer, the modem discards all data in that frame.
If the modem receives any character from the DTE after the +FRH 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 OK result code, and returns to command mode. The receive buffer is cleared and all
data received from the remote is discarded. If the modem detects a DTR drop while &D2 is in effect, it goes on-hook, sends
<DLE><ETX> to the DTE, generates OK result code, and returns to command mode. If the modem detects a DTR drop
while &D3 is in effect, the modem performs a warm reset.
5.1.8 Fax Data Transmission
Fax data transmission is initiated by the AT+FTM=n command. After this command is issued, the modem generates the
CONNECT message and transmits carrier in the modulation scheme specified by the parameter n. The modem then
transmits constant 1 bits for a minimum of one second and continues to transmit constant 1 bits until it receives a character
from the DTE.
When data is received from the DTE, the modem deletes start and stop bits and deletes all <DLE><chr> character pairs
before transmitting the data to the remote. Each <DLE><DLE> sequence is transmitted as a single <DLE>. <DLE><ETX> is
considered 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.
5.1.9 Fax Data Reception
Fax data reception is initiated using the AT+FRM=n 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.