Calling Line Identifier with VMWI
CMX612
td = Internal CMX612 delay; max. 1mS
tclo = RXCK low time; min 1mS
tchi = RXCK high time; min 1mS
Figure 5a : FSK Operation With Data Retiming
Note that, if enabled, the Data Retiming block will interpret the FSK Channel Seizure signal (a sequence
of alternating mark and space bits) as valid received characters, with values of 55 (hex). Similarly it may
interpret speech or other signals as random characters.
If the Data Retiming facility is not required, the RXCK input to the CMX612 should be kept high. The
asynchronous data from the FSK Demodulator will then be connected directly to the RXD output pin, and
the IRQN output will not be activated by the FSK signal. This case is illustrated in Figure 5b.
Figure 5b : FSK Operation Without Data Retiming (RXCK always high)
1.5.7 Tone Alert Detector
This block is enabled when the CMX612 is set to Tone Alert Detect mode. It will then monitor the
received signal for the presence of simultaneous 2130Hz and 2750Hz tones of sufficient level and
duration.
Two digital bandpass filters, centred around 2130Hz and 2750Hz, are used within the block to give
additional rejection of interfering signals.
The CMX612 DET output will be set high while a Tone Alert signal is detected. At the end of the Tone
Alert signal the detector will derespond in 5ms typically. Since the deresponse time is governed by a
statistical process, there will be occasions when the maximum figure of 17ms is exceeded.
When the DET output goes low at the end of the Tone Alert signal, then if the DET output had been high
for a time within the CAS qualifying time TqCAS limits (see Section 1.7.1) , then the IRQN output will be
pulled low and will remain low until the CMX612 is switched out of Tone Alert Detect mode. Note that the
TqCAS timing has been optimised for the detection of 75 to 85ms Tone Alert (CAS) signals used in off-
ã 2002 Consumer Microcircuits Limited
10
D/612/3
CMLMICRO [ CML MICROCIRCUITS ]
