CMX868 Reference Design and Demonstration Board
DE8681
The Dial and Answer commands will execute the relevant DTMF transmit, call progress tone
detection and negotiation (handshaking) firmware routines before a connection to a remote
modem/simulator can be established. Negotiation may be aborted by pushing any key.
Note, if the S0 register is modified to a non-zero value during this operating mode, the CMX868
status register will be polled every 20ms to check for ring detect status. If valid ringing is
detected the DE8681 will automatically answer a call after n ring cycles, where n is equivalent to
the contents of the S0 register.
Data Transfer Mode
After gaining a connection (i.e. successful negotiation) with a remote modem the board will be
operating in data transfer mode. In this mode the board will transmit all the data it receives from
the RS232 computer terminal to the remote modem via the 2-wire line. Likewise any data
received from the remote modem via the 2-wire line will be sent to RS232 computer terminal.
Whilst operating in this mode the data stream from the RS232 computer terminal is monitored for
the escape code sequence (+++). If this sequence is encountered during data transfer the
firmware will revert to on-line AT command mode. Whilst in on-line, AT command mode, the
board to remote modem connection may be aborted by typing ATH0 (instructs modem to go on-
hook). Alternatively the user can enter relevant AT commands or return to data transfer mode by
using the ATO command.
The modem line speed is much lower than the speed of the RS232 interface (RS232 is running at
19200bps) and the DE8681 firmware only provides a small amount of data buffering. Therefore
to prevent the data buffer from overflowing the data flow between the µC and RS232 is controlled
by the RTS/CTS (Request/Clear to Send) hardware handshake lines.
The CMX868 settings used during negotiation and data transfer will be based on the contents of
the S-registers when the call was originated or answered. The S-registers are described in
Section 1.6.3. Certain S-register settings (relevant to the CMX868 configuration), modified
during on-line AT command mode, will only take effect when a new call is originated or
answered. For example, new CMX868 Tx gain settings (S25 register) modified in on-line AT
command mode will be ignored until the next call.
ã 2004 CML Microsystems Plc
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UM8681/3
CMLMICRO [ CML MICROCIRCUITS ]
