Evaluation Kit for CMX868

EV8680

© 2000 Consumer Microcircuits Limited

6

UM8680/2

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

EV8680 Evaluation board 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 EV8680 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.