Calling Line Identifier
CMX602A
td = Internal CMX602A 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 CMX602A 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 CMX602A is set to Tone Alert Detect mode. It will then monitor the received
signal for the presence of simultaneous 2130 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 CMX602A DET output will be set high while a Tone Alert signal is detected.
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 1.7.1) , then the IRQN output will be pulled low and will
remain low until the CMX602A 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-hook applications, the longer (88
to 110ms) Tone Alert signal employed by BT for on-hook applications will not necessarily cause IRQN to go
low.
ã 1998 Consumer Microcircuits Limited
10
D/602A/4
CMLMICRO [ CML MICROCIRCUITS ]
