CMX602BD4 MX-COM, Inc., CMX602BD4 Datasheet - Page 11

• Manufacturer Part Number: CMX602BD4
• Description: Calling line identifier plus call waiting
• Manufacturer: MX-COM, Inc.

Calling Line Identifier plus Call Waiting (Type II)
When no signal is present on the telephone line, RD will be at V
of the Schmitt trigger 'B' will be low.
The ring signal is usually applied at the subscriber's exchange as an ac voltage. The ring signal is inserted in
series with one of the telephone wires and will pass through either C3 and R3 or C4 and R4 to appear at the
top end of R1 in a rectified and attenuated form.
The signal prior to R1 will be further attenuated by the potential divider formed by R1 and R2 before being
applied to the CMX602B input RD. If the amplitude of the signal appearing at RD is greater than the input
threshold (Vt
voltage at RT to V
go high, activating the DET and/or IRQ outputs depending on the states of the MODE and ZP inputs.
The minimum amplitude ringing signal that is certain to be detected is:
With R1, R3 and R4 all 470k as indicated in Figure 2, then setting R2 to 68k will guarantee detection of
ringing signals of 40V
A line polarity reversal may be detected using the same circuit but there will be only one pulse at RD. The
British Telecom specification SIN242 indicates that the circuit must detect a +15V to -15V reversal between
the two lines slewing in 30ms. For a linearly changing voltage at the input to C3 (or C4), then the voltage
appearing at the RD pin will be
For dV/dt = 500V/sec (15V in 30ms), R1, R3 and R4 all 470k and C3, C4 both 0.1 F as indicated in Figure
2, then setting R2 to 390k will guarantee detection at V
If the time constant of R5 and C5 is large enough then the voltage on RT will remain below the threshold of
the 'B' Schmitt trigger keeping the DET and/or IRQ outputs active for the duration of a ring cycle
The time for the voltage on RT to charge from V
As the Schmitt trigger high-going input threshold voltage (Vt
Schmitt trigger 'B' output will remain high for a time of at least 0.821 x R5 x C5 following a pulse at RD.
Using the values provided in Figure 2 (470k and 0.33 F) gives a minimum time of 100ms (independent of
V
If necessary, the µC can distinguish between a ring and a reversal by timing the length of the IRQ or DET
output.
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), which is adequate for ring frequencies of 10Hz or above.
Where Vt
HI
) of Schmitt trigger 'A' then the N transistor connected to RT will be turned on, pulling the
SS
HI
by discharging the external capacitor C5. The output of the Schmitt trigger 'B' will then
RMS
is the high-going threshold voltage of the Schmitt trigger A (see Section 6.1).
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where T
and above for V
0.7 Vt
C3 R1 R2 R3 and
DD
V
HI
RT
dV
= 2.7 to 5.5V.
dt
R1 R2 R3
SS
C3 1 e
V
DD
towards V
R2
11
1 e
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dV
T
= 5.5V.
HI
t
dt
R5C5
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) has a minimum value of 0.56 x V
R2
0.707V
t
is the input slew rate.
SS
can be derived from the formula
and RT pulled to V
RMS
CMX602B PRELIMINARY INFORMATION
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by R5 so the output
Doc. # 20480204.002
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, then the