r6781-12 Conexant Systems, Inc., r6781-12 Datasheet - Page 68

• Manufacturer Part Number: r6781-12
• Description: Embedded Modem Family
• Manufacturer: Conexant Systems, Inc.

6.2 Fax Modes
6.2.5 Fax Data Transmission
6.2.6 Fax Data Reception
6.2.7 Fax Control Transmission
6-4
Fax data transmission is initiated by the +FTM command. Upon recognition of
the command, the modem initiates the selected modulation mode and issues the
CONNECT result code. The proper training sequence for the selected mode is
transmitted, followed by constant 1 bits, until data is received from the DTE. DTE
data is buffered and processed prior to being transmitted. The transmission is
terminated when the transmit buffer becomes empty and the last transmitted
character was not a NUL character. The modem then turns off the carrier and
issues the OK result code. If the last character was a NUL character (00), the
modem continues to transmit NUL characters until more data is received by the
DTE or until 5 seconds have elapsed. After 5 seconds, the modem turns off the
carrier and issues the ERROR result code.
Fax data reception is initiated by the +FRM command. Upon recognition of the
command, the modem initiates the selected demodulation mode and looks for the
proper carrier. When the selected carrier is detected, the modem issues the
CONNECT result code +FCERROR. If a signal other than the selected carrier is
detected, the modem returns to the command state. Demodulated data is stored in
an output buffer for additional I/O processing and eventual output to the DTE.
Detection of loss of carrier will cause the modem to issue the NO CARRIER
result code and will cause the modem to return to the command state. Any
character other than flow control characters issued while the receiver is outputting
data will cause the receiver to abort and return to the command state.
Fax control transmission is initiated by the +FTH command or after answering a
call. The modem initiates the selected modulation mode, issues the CONNECT
result code, transmits one second of flags, then transmits data sent by the DTE.
DTE data is buffered and processed prior to transmission.
The generator polynomial is X
sequence (FCS) is appended to the end of the frame. The end of the frame is
indicated by an empty I/O buffer. Transmission frames begin and end with a flag
sequence (7Eh). The ending flag may serve as the beginning flag for the next
frame. To prevent data from looking like flags, a 0 is inserted into the data stream
after five consecutive 1s are detected.
Processed I/O data is grouped into frames and encoded with a CRC generator.
Conexant
16
+ X
12
+ X
5
+ 1. The CRC parity or frame check
EmbeddedModem Family
D224ATLVDSC