Dual SPM/Security Detector/Generator
CMX641A
modulated on-off by the TONE ASK pin. A high (logic ‘1’) selects no tone and low (logic ‘0’) selects tone.
The transmission frequency is selected by the TX TONE SELECT pin. A high (logic ‘1’) selects 12kHz
and a low (logic ‘0’) selects 16kHz. (See Table 7).
Output Select Circuits
These drive the output logic pins ‘Channel 1 Output’ (CH1OP) and ‘Channel 2 Output’ (CH2OP). These
outputs can be made high impedance by setting the OP ENABLEN pin high. When enabled, the format
at these pins is either Tone Follower or Packet. (See Table 1). A high (logic ‘1’) indicates the tone is
absent, a low (logic ‘0’) indicates the tone is present.
1.5.2 Operating States
There are two operating states for the CMX641A: Fixed Bandwidth and Enhanced Features.
Fixed Bandwidth Operating State (ENHANCED FEATURES pin = logic ‘0’ or open circuit)
In this operating state, the CMX641A is function and pin compatible with the FX641 and MX641. It is a
dual-channel SPM detector with both detectors set to the same level sensitivity and system frequency
(12kHz or 16kHz) via a 6-bit serial data word from a host µController. Alternatively, for non µController
systems, the sensitivity and system frequency can be set via external components and logic inputs. In
this state, the decode bandwidth of both channels is internally fixed at ±1.5% of the nominal centre
frequency.
Enhanced Features Operating State (ENHANCED FEATURES pin = logic ‘1’)
In this state, the following features of the two SPM detector channels are independently controllable via a
16-bit serial data word from a host µController.
(i)
The decode bandwidths, which can be set to ±1.5%, ±3%, ±5% and ±7.5% of the nominal
tone frequency.
(ii)
The level sensitivity.
(iii)
The system frequencies, which have one of three possible settings: 12kHz & 12kHz, 16kHz &
16kHz, or 12kHz for Channel 2 and 16kHz for Channel 1.
When the two channels are set to 12kHz/16kHz mode, there is an option to disconnect the channel 2
decode path from its own amplifier and have both channels connected to the channel 1 input. The
channel 2 amplifier is then independent and available for some other use, say gain setting or filtering,
within the host circuitry.
There is also a transmit tone, selectable to 12kHz or 16kHz, which is ASK modulated via a logic input pin.
Features Common to both Operating States
In both states, three output formats are available for the channel output pins. These output formats are
selectable via the logic input pins OP SELECT and OP ENABLEN. (See Table 1).
(i)
In Tone Follower mode, the logic output has very short response and deresponse times so
that it forms an ‘envelope’ of the input tone. Host systems will decide whether the received
signal fulfils the system tone pulse length requirements.
(ii)
In Packet mode, the channel output only responds after 40ms of received continuous tone.
The CMX641A then ignores the erroneous 20ms on, 20ms off “ringing” pattern which occurs
on some telephone lines.
(iii)
The deresponse time is also 40ms, so that the decode output pin forms a delayed envelope
of the input tone and host systems can decide, as in the Tone Follower mode, whether the
received tone duration fulfils local system requirements.
ã 2002 Consumer Microcircuits Limited
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D/641A/5
CMLMICRO [ CML MICROCIRCUITS ]
