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CT104 (RXD) received data:
Digital information that is received and demodulated.
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CT105 (RTS) request to send:
The MLU wants to send digital information and initiates a request towards the modem.
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CT106 (RFS) ready for sending:
If the MLU initiated a send request and the modem is able to send the digital information,
the ready for sending signal indicates to the MLU that the information can be transmitted.
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CT107 (DSR) data set ready:
This signal indicates that the analogue line is switched from the telephone to the modem.
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CT108.1 (CDSL) connect data set to line
The command from the MLU towards the modem to switch the analogue line from the
telephone set to the modem.
It is not possible to use the CT108.2 (DTR) signal. This signal is just an indication to the
modem the MLU is ready for operation. By means of a second condition (manual switch
over or ring indicator) the modem switches the telephone line from the telephone to the
data port. Because the ring indicator signal (CT125) is not supported by the MLU and
because the modem must operate in the unattended mode this second condition cannot
be fulfilled. CT108.1 (CDSL) must be used: this signal is a real command which does not
need a second condition.
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CT109 (DCD) data carrier detect:
This signal indicates to the MLU that an incoming carrier signal is detected.
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CT111 (DSRS) data signal rate selection:
If the modem offers the possibility to operate with a high or a low speed, the MLU is able
to select the high or the low speed by means of this signal. The lower speed can be
selected if there are too many transmission errors detected.
If this signal is true the high transmission speed is selected in the modem.
If this signal is false the low transmission speed is selected in the modem.
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CT113 (TSET) transmit signal element timing:
Only used in synchronous transmission. The MLU provides the transmit clock for the
modem.
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CT115 (RSET) receive signal element timing:
Only used in synchronous transmission. The modem sends the clock signal retrieved from
the incoming data stream to the MLU.
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CT126 (STF) select transmit frequency:
For an incoming call the modem receives data in the low frequency band (forward
channel) and sends in the high band (backward channel).
For an outgoing call the modem sends in the low frequency band (forward channel) and
receives in the high band (backward channel).
By means of this signal the MLU can determine if the modem sends in the low or in the
high band.
If this signal is true the high frequency band is selected for transmitting data (answering
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