CML Microcircuits CMX866, Manual, Page: 19 / 53

V.22 bis Modem with AT Commands CMX866
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2008 CML Microsystems Plc 19 D/866/5
&Dn Register
Parameter DTR action
n (Mapped to S24 register)
0 Ignore DTR signal
1 Go to command state when on to off transition occurs
2 Hang up and go to command state when on to off transition occurs
&Gn Register
Parameter Guard Tone action
n (Mapped to S23 register)
0 Disabled
1 Enabled 550Hz
2 Enabled 1800Hz
&Tn Register Parameter Test function
n (Mapped to S21 register)
0
Terminate test
1
Reserved
2
Reserved
3
Local digital loopback
4
Enable remote request for digital loopback
5
Disable remote request for digital loopback
6
Request remote digital loopback & initiate
1.5.4.2 General Description of AT Commands
Only the AT commands listed above are supported. Valid commands will generate an 'OK' result code
(see section 1.5.4.6) and invalid commands will be rejected with an 'ERROR' result code, when command
echoing and word result codes are enabled. The on-chip µController will send a <LF> character directly
after a <CR> character to ensure compatibility with external host µControllers. Any commands which are
not fully implemented will return the result code ‘NYI’ (Not Yet Implemented). AT commands should not
be sent to the on-chip µController until the previous result code (if enabled) has been received.
Every line of commands (except for A/ and the escape sequence) must begin with the AT prefix and be
terminated with a carriage return <CR>. The on-chip µController waits to receive a complete AT
command line before processing it. Embedded spaces are ignored and the case (upper or lower) of
characters including the ‘AT’ does not matter. The command line must not exceed 48 characters
(excluding the ‘AT’ characters). The on-chip µController will ignore the command line and return an
'ERROR' result code if the line is not terminated correctly.
All characters in the AT command, including the ‘AT’ and <CR> terminator are echoed (if E1 is set) by the
CMX866 in the order in which they are sent by the external host µC.
If when entering an AT command, no command or register name suffix is supplied, a suffix of zero is
assumed. If when changing a register value, no value is supplied a value of zero or an empty string is
assumed: eg ATS0=<CR> is equivalent to ATS0=0<CR>.
Receipt of a back space will cause the CMX866 to send a "back space, space, back space" sequence of
characters to the external host µC, to allow any terminal which may be connected to the latter to clear its
screen of the last character. Also the last character received will be discarded unless the last characters
received were ‘AT’, ie the ‘AT’ is never deleted.