V.22 bis Modem with AT Commands
CMX866
1.5
General Description
1.5.1 Internal Structure
Internally, the CMX866 consists of a dedicated DSP which is controlled by an on-chip µController. This
µController is preprogrammed to interpret the AT commands provided by the user into instructions for
controlling the dedicated DSP. It also handles the CMX866 power management and other functions. The
DSP is preprogrammed with algorithms to implement the various modem functions, but also has Tone
Generators and Detectors which are user programmable with AT commands, via the on-chip µController.
The CMX866's DSP transmit and receive operating modes are independently programmable by means of
AT commands which write values into the S-Registers. The on-chip µController then interprets the
values in these registers and programs the corresponding registers in the dedicated DSP.
The DSP transmit mode can be set to any one of the following:
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V.22 bis modem. 2400bps QAM (Quadrature Amplitude Modulation)
V.22 and Bell 212A modem. 1200 bps DPSK (Differential Phase Shift Keying)
V.21 modem. 300bps FSK (Frequency Shift Keying)
Bell 103 modem. 300bps FSK
V.23 modem. 1200 or 75 bps FSK
Bell 202 modem. 1200 or 150 bps FSK
DTMF transmit
Single tone transmit (from a range of modem calling, answer and other tone frequencies)
User programmed tone or tone pair transmit (programmable frequencies and levels)
Disabled
The DSP receive mode can be set to any one of the following:
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V.22 bis modem. 2400bps QAM
V.22 and Bell 212A modem. 1200 bps DPSK
V.21 modem. 300bps FSK
Bell 103 modem. 300 bps FSK
V.23 modem. 1200 or 75 bps FSK
Bell 202 modem. 1200 or 150 bps FSK
DTMF detect
2100Hz and 2225Hz answer tone detect
Call progress signal detect
Dual alert tone pair detect (for Caller Line Identification)
User programmed tone or tone pair detect
Disabled
The CMX866 can also be set into 'Zero-Power' or Powersave states, which disable all circuitry except for
the Ring Detector. The S-Register settings and the CMX866's configuration are remembered when in
'Zero-Power' or Powersave states. The 'Zero-Power' state stops the crystal oscillator and removes power
from the VBIAS pin, for minimum power consumption. It takes about 30ms for the CMX866 to become
operational from the 'Zero-Power' state. The Powersave state stops the internal clock distribution, but
retains power to the crystal oscillator and VBIAS circuit. Consequently, the CMX866 can become
operational from this state in about 10µs. If the TXD pin is tied to the DTRN pin (to implement a reduced
RS232 interface) any activity on the TXD pin will also take the CMX866 into an operational state. In this
case, however, data may be corrupted until the CMX866 is fully operational.
ã 2004 CML Microsystems Plc
13
D/866/4
CMLMICRO [ CML MICROCIRCUITS ]
