Q. I am interested in using the programmable tone detection feature of the chip. Do you have any tools to help me calculate the required coefficients?
A. The CMX868 filter coefficient generator spreadsheet can also be used for the CMX866, and this spreadsheet can be found at: http://www.cmlmicro.com/products/applications/WirelineFL_1.htm..
Q. How can I use the CMX866 in a leased line configuration?
A. If you need a permanent or part time connection between two modems, a leased line is a popular option. In most leased line applications both the answering and originating modems are left in the off-hook state indefinitely. This means that even when data is not being sent, there will still be activity in the form of a carrier signal. If the line is broken for some reason, the modems should detect this, go on-hook, and re-establish the link.
The interface from modem to leased line can be either 4 line of 2 line (usually 4), and the modulation methods and protocols are typically already known on both ends of the link.
To achieve a successful connection the modem must go off-hook and immediately start a handshake (V.23, V.22 or V.22bis are typical). No dial tone, ring back or busy tones will be present on the line and the 2100Hz answer tone may not be present. Additionally, as there is no direct way of initiating the sequence with the answering modem (no ringing signal is generated at the answering modem), the modem must test the line (typically every 30 seconds or so) whilst the line is idling (before data or carrier signal is present).
To establish a link with the CMX866 in originating mode:
A TX=0 ;Blind dialing; the modem is told not to expect a dial tone when going off hook.
S6= 0; No wait for dial tone; we want the modem to try and connect immediately.
ATD1; Go off hook, dial DTMF digit and attempt to connect to the answering modem (detects 2100Hz or scrambled 1's).
S7 = >30 and <50sec ;wait 30 seconds, if modem not present wait a further 20 seconds and repeat.
To establish a link with the CMX866 in answering mode:
Establish a >30 second timer
Off-hook and Generate Answer Tone: ATA
If no connection is established, re-establish the 30 second timer.
All other settings such as V.22bis, gain etc should remain the same as normal.
Q. I am using the CLI code available in your Applications Note section on your website (http://www.cmlmicro.com/products/applications/866_CLI_2.PDF); however I do not have access to the RESETN pin in my design and wish to re-enter AT command Mode following CLI decoding?
A. It is possible to re-enter AT command mode without issuing RESETN, following CLI routine execution as the interpreter is based on an 8051 core. It is achieved by inserting a long jump command (LJMP) to 1000h at the end of the exit routine in the CLI routine hex dump. This has not been tested by CML but has been shown to work.
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