Product data

USRobotics
Command Reference
Fax Class 1 and Fax Class 1.0 Commands - 110
transmits carrier in the modulation scheme specified by the parameter n. The
modem then transmits HDLC flags for a minimum of 1 second. The modem
continues to transmit the HDLC flags until it receives a character from the DTE.
When characters are received from the DTE, the modem adds start and end flags,
performs zero-bit insertion, generates FCS, and deletes <DLE><chr> character
pairs before transmitting the characters to the remote fax machine. Each
<DLE><DLE> sequence is transmitted as a single <DLE>. <DLE><ETX> is
considered as the end of frame marker and is not transmitted. All data received
from the DTE after <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 final bit was a 1 (bit 4 of the
second byte received from the DTE), the modem generates the OK result code
and returns to the command mode. If the final bit was a 0, the modem generates
the CONNECT message and waits for further data from the DTE while
transmitting HDLC flags. If no more data is received before 5 seconds elapse, the
modem drops carrier, goes on-hook, and generates the ERROR result code.
Fax Control Reception
Fax control reception is initiated using the AT+FRH=<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 carrier is detected that is not the one
specified by the parameter n, 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 HDLC receive mode.
In HDLC receive mode, the modem receives HDLC frames from the remote fax
machine, strips the flags, performs zero-bit deletion, performs error checking, 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. After the last byte in the frame, the modem sends
<DLE><ETX> to the DTE marking the end of the frame.
The modem then generates either the OK message if no errors were detected or
the ERROR message if errors were detected (FCS is incorrect), and returns to
command mode.
While in command mode, the modem continues to receive data in the selected
modulation scheme, and sends the data after sending the CONNECT message to
the DTE when the DTE reissues the +FRH command with the same parameter. If
the DTE issues the +FRH command with a different parameter, the modem clears
all buffers and proceeds as described previously.
If carrier is lost while in command mode and the DTE reissues the +FRH
command with the same parameter, and there is no data in the buffer, the modem
sends the ERROR result code to the DTE and returns to the command mode. If
there is data in the buffer, the modem sends the next frame of buffered data to the
DTE, followed by <DLE><ETX>, and either the ERROR result code if errors were
detected or the OK result code if no errors were detected. The modem then