SI3015-F-FS Silicon Laboratories Inc, SI3015-F-FS Datasheet - Page 20

• Manufacturer Part Number: SI3015-F-FS
• Description: IC ISOMODEM LINE-SIDE 16SOIC
• Manufacturer: Silicon Laboratories Inc
• Type: Chipsetr

Specifications of SI3015-F-FS

• Package / Case: 16-SOIC (3.9mm Width)
• Data Format: V.90
• Interface: Serial
• Voltage - Supply: 3.3 V ~ 5 V
• Mounting Type: Surface Mount
• Product: Modem Chip
• Supply Voltage (min): 3 V
• Supply Current: 26 mA
• Maximum Operating Temperature: + 70 C
• Minimum Operating Temperature: 0 C
• Mounting Style: SMD/SMT
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Baud Rates: -
• Lead Free Status / Rohs Status: Compliant

Si2400
5.5.5. Differential Algorithm #2
This differential algorithm has features added to
Differential Algorithm #1. The additional features are as
follows:
5.5.6. Deglitch Filter
To avoid triggering an off-hook intrusion interrupt due to
a transient or glitch on the telephone line, a deglitch
filter is inserted before the off-hook intrusion algorithm.
The sample rate of
SDF[6:0] (DGSR).
Algorithm #1 is implemented.) Before a sample is
passed to the off-hook intrusion algorithm, it must be
confirmed by a subsequent sample of the same value.
Otherwise, it is not submitted to the off-hook algorithm.
In order to filter out glitches of up to 1 second in
duration, for example, DGSR should be set to 1 second
(SDF[6:0] = 011001b). In this example, an intrusion
event that lasts for more than two seconds is
guaranteed to be treated as a real intrusion. Intrusion
events between one second and two seconds in
duration may or may not be treated as an intrusion. The
recommended setting for DGSR is one second, which
should work for most applications.
Once a sample has been deemed valid by the deglitch
filter, the off-hook algorithm operates as follows:
If (LVCS (t – 80 ms DGSR) – LVCS (t)) > DCL, then an
intrusion is deemed to have taken place. Default DCL
is 2. This comparison occurs every 40 ms DGSR.
Because the compared value is continually updated, the
off-hook intrusion algorithm automatically adjusts to
account for drift in line resistance.
5.5.7. LVCS Initialization
If an intrusion begins within the time window defined by
S82[7:4] (IST), it is possible for an intrusion to go
unreported because the initial LVCS used as the
reference is sampled after the intrusion has begun.
S12[4:0] (ACL) is used to avoid this problem. Prior to
going off-hook, the host can set the ACL register to a
known value of LVCS with the Si2400 off-hook and all
parallel phones or other devices on-hook. If this value is
not known, such as on the first off-hook event using this
specific phone line, ACL should be set to 0, indicating
no known LVCS reference.
Once the Si2400 goes back on-hook, it automatically
writes the value of the last known LVCS sample prior to
20
Programmable deglitch filter to minimize false
intrusions
Ability to preset initial LVCS reference prior to going
off-hook
Optional time window where intrusions are blocked
and ignored
(If
DGSR = 0,
the deglitcher is set by
the
Differential
Rev. 1.3
an intrusion, if any, into ACL. Therefore, ACL may be
used for the next off-hook event even if the current off-
hook sample contains an intrusion. Except for the first
initialization, no host intervention is necessary.
The Si2400 clears ACL automatically under a hardware
reset. Additionally, ACL is cleared if the modem is on-
hook, and the phone line is disconnected and then
reconnected once again.
If the host hardware resets the Si2400 between off-hook
events, the host may choose to store the ACL value
prior to reset, and then restore this value to ACL prior to
the next off-hook event.
5.5.8. Intrusion Blocking
Differential Algorithm #2 may be disabled for a period of
time after dialing begins. This can avoid triggering an
off-hook intrusion interrupt due to pulse dialing or line
transients from central office switching. The method to
block the intrusion algorithm is set via S82[1:0] (IB). If
IB = 10b is chosen, S29 (IS) can be used to set this
blocking to an absolute time.
In order to detect if an intrusion does occur during
blocking and is sustained until after the blocking, the
Si2400 will measure the difference in LVCS between the
sample before blocking and the sample after blocking.
5.5.9. Absolute Algorithm
If the absolute detector is chosen (S13[4] [OFHD] = 0
the Si2400 will detect an intrusion under the condition
that LVCS is less than the off-hook intrusion threshold,
S12[4:0] (ACL). In other words, it is determined that an
intrusion has occurred if LVCS < ACL. ACL defaults to 0
(12 mA) on powerup. Because the loop current can vary
from 20 mA to 100 mA, depending on the line, a factory
preset threshold is not useful.
To use this absolute mode, the host must measure the
line current and set the threshold accordingly. A
measurement of the loop current is accomplished by
going off-hook (issuing the “ATDT;” command), reading
LVCS after 800 ms, and going back on hook using the
“ATH” command. This measured value of LVCS should
be used to determine the threshold register ACL. If this
method is used, the loop current should be measured
on a periodic basis to account for drift in line resistance.
5.5.10. Reporting Off-Hook Intrusions
The primary method of reporting an off-hook intrusion
event to the host is through the use of the ALERT pin.
The ALERT function is assigned to GPIO4 by setting
SE2[7:6] (GPIO4) = 11b.
In general, “i” and “I” result codes are sent when the
modem detects an intrusion. However, it is important to
note that these result codes are not always reported.
When the modem is in the data mode, the “i” and “I”
b
),