SI3200-X-FS SILABS [Silicon Laboratories], SI3200-X-FS Datasheet - Page 46

• Manufacturer Part Number: SI3200-X-FS
• Manufacturer: SILABS [Silicon Laboratories]

Si3220/25
The output of the debounce filter remains in its present
state unless the input remains in the opposite state for
the entire period of time programmed by the loop
closure debounce interval, LONGDBI. If the debounce
interval is satisfied, the LONGHI bit is set to indicate
that a valid ground key event has occurred.
When the Si3220/25 detects a ground key event, the
linefeed automatically transitions from the TIP-OPEN
(or RING-OPEN) state to the FORWARD-ACTIVE (or
REVERSE-ACTIVE) state. However, this automatic
state transition is triggered by the LCR bit becoming
active (i.e., =1), and not by the LONGHI bit.
While I
a transition from TIP-OPEN to the FORWARD-ACTIVE
state (or from the RING-OPEN to the REVERSE-
ACTIVE state) occurs when the RING terminal (or TIP
terminal) is grounded and is based on the LCR bit and
implicitly on exceeding the LCROFFHK threshold.
As an example of ground key detection, suppose that
the Si3220/25 has been programmed with the current
values shown in Table 25.
With the settings of Table 25, the behavior of I
I
Table 26. The entries under “Loop State” indicate the
condition of the loop, as determined by the equipment
terminating the loop. The entries under “LINEFEED
Setting” indicate the state initially selected by the host
CPU (e.g., TIP-OPEN) and the automatic transition to
the FORWARD-ACTIVE state due to a ground key
event (when RING is connected to GND). The transition
from state #2 to state #3 in Table 26 is the automatic
transition from TIP-OPEN to FWD-ACTIVE in response
to LCR = 1.
46
LONG
Table 25. Settings for Ground Key Example
, LCR, LONGHI, and CMHIGH is as shown in
LONG
is used to generate the LONGHI status bit,
LONGLOTH
LCROFFHK
LONGHITH
LCRONHK
ILIM
21 mA
14 mA
10 mA
7 mA
5 mA
LOOP
Rev. 1.2
,