U3900BM
2.2.6
Down Guard Time, Description
2.2.7
Wetting Pulse Function
The down guard time circuitry prevents drops from
speech or music (talk-down).
The input signal (both 2130 Hz and 2750 Hz) must be
continuously low for a duration depending on the
2 programmable bits DGT0 and DGT1.
The early guard time is used like for up guard time, but
the drop counter is not activated.
* Note:
The Idle State is an electrical condition into which the TE
(when connected to the network) is placed such that it
draws minimum current and does not activate the
exchange.
DGT0
0
1
0
1
DGT1
0
0
1
1
DGT Value
15 ms
17 ms
18 ms
19 ms
British Telecom states that the TE is required to apply a
DC wetting pulse and an AC load 205 ms after the end of
the alerting signal (the Idle State* Tone Alert Signal); the
duration of the wetting pulse is 151 ms; the TE shall rise
to a minimum of 25 mA and maintain that current for a
total time of not less than 5 ms.
OCTEL3 provides a 15-ms counter (which starts at the
end of the alerting signal delayed by the down guard time
value) to help the microprocessor to fulfil this
requirement.
The signals at the output of the guard time system are sent
to the SSB-INTERRUPT treatment.
An interrupt occurs at each edge of the OUT SCWID
detector.
When the wetting pulse is enabled (CDE8. mode
UK = 1), an interrupt is sent to the microprocessor 15 ms
after the falling edge of the WP detector.
Idle state tone alert signal duration: 100
±10
ms
frequencies: 2130 Hz + 2750 Hz
IN SCWID
detector
Choice of 4
UGT values
Up guard
time
OUT SCWID
detector
OUT WP
detector
Choice of 4
DGT values
Down guard
time
Interrupt
to the
µP
15 ms
Interrupt
to the
µP
WETTING PULSE
(Under
µP
control)
20
±
5 ms
Interrupt
to the
µP
15
±
1 ms
Current that
TE shall draw
Not less
than 25 mA
Not less
than 5 ms
14607
Figure 7. Alert detection timing diagram with wetting pulse
Rev. A2, 25-Aug-98
9 (34)
Target Specification
TEMIC [ TEMIC SEMICONDUCTORS ]
