Intel 537EX User Manual

68

Receive HDLC Data: The +FRH=<mod> command causes the modem to receive 
HDLC-framed data using the modulation mode selected in <mod>. The modem then 
delivers the next-received frame to the DTE.

If the modem detects the selected carrier signal with an HDLC flag, the modem sends 
a ‘CONNECT’ result code to the DTE. If the modem detects a different signal, the 
modem sends the ‘+FCERROR’ (fax connect error) result code to the DTE and returns 
to command mode. Upon loss of carrier, the modem returns to command mode and 
sends a ‘NO CARRIER’ result code to the DTE.

After receiving the HDLC flags, the modem strips away the flags and buffers the 
received frames. The modem then transfers the received data to the DTE, starting with 
the first non-flag byte and continuing through the last FCS byte. The DTE should 
ignore the value of the FCS bytes. The modem also performs HDLC zero-bit deletion 
and error checking.

After the FCS bytes are transferred, the modem marks the end of the frame with 

<DLE><ETX> 

and reports the status of the frame reception to the DTE. If the frame 

was received correctly (FCS is correct), the modem returns a ‘OK’ result code. If the 
frame was received in error (FCS is not correct, carrier lost, or data lost due to data 
overflow), the DCE returns an ‘ERROR’ result code. The DTE should then discard this 
frame.

After sending the status result code, the modem is ready to accept new commands 
from the DTE.

The modem obeys the configured flow control from the DTE. If the DTE sends any 
character to the modem other than DC1 or DC3 while the modem is in this mode, the 
modem enters command mode and return an ‘OK’ result code.

After sending the result code indicating that frame reception is complete, the modem 
continues to receive and buffer the data in the selected mode. If the DTE issues 
another +FRH=<mod> command, the modem returns another ‘CONNECT’ result 
code and continues with HDLC reception. If the DTE issues any command that 
changes modulation, the DCE stops the receive process; the DCE then discards any 
buffered data and processes the command.

Range: <mod> = 3

Refer to 

Receive Data: The +FRM=<mod> command causes the modem to enter receive 
mode using the modulation scheme specified in <mod>. <mod> may have the values 
shown in 

When the selected carrier is detected, the modem sends a ‘CONNECT’ result to the 
DTE. If a different signal is detected, the modem sends a ‘+FCERROR’ (connect error) 
result code to the DTE and returns to command mode.

After receiving the selected carrier, the modem transfers all received data patterns to 
the DTE as consecutive start-stop framed bytes, including leading marking conditions 
or flags. The modem marks the end of the data stream with 

<DLE><ETX>

.

Upon loss of carrier, the modem returns to command state and sends a ‘NO 
CARRIER’ result code to the DTE.
NOTE: If the modem is on-hook, then the modem always returns an ‘ERROR’ 

message to the DTE after receiving the +FRM=<mod> command.

Range: <mod> = 24, 48, 72, 73, 74, 96, 97, 98, 121, 122, 145, 146

Refer to 

Wait for Silence: The +FRS=<TIME> command causes the modem to send an ‘OK’ 
result code to the DTE when silence has been detected on the line for the amount of 
time specified. The value <TIME> is in 10 ms intervals. The command terminates 
when the required amount of silence has been detected on the line or the DTE sends 
the modem another character that is discarded. In either event, the DTE returns the 
‘OK’ result code.

Range: <TIME> = 1–255 (10 ms)

NOTE: An asterisk (*) denotes the factory-default setting.