
Si3220/25 Si3200/02
Rev. 1.3
61
Not
Recommended
fo
r N
ew
D
esi
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Setting the linefeed register to the opposite polarity
immediately reverses (hard reversal) the line polarity.
For example, to transition from Forward Active mode to
Reverse Active mode changes LF[2:0] from 001 to 101.
Polarity reversal is accommodated in the OHT and
ground start modes. The POLREV bit is a read-only bit
that reflects if the device is in polarity reversal mode.
For smooth polarity reversal, set the PREN bit to 1 and
the RAMP bit to 0 or 1 depending on the desired ramp
rate
(see
Polarity
reversal
is
then
accomplished by toggling the linefeed register from
forward to reverse modes as desired.
A wink function slowly ramps down the TIP-RING
voltage (VOC) to 1 followed by a return to the original
VOC value (set in the VOC RAM location). This scheme
lights a message-waiting lamp in certain handsets. No
change to the linefeed register is necessary to enable
this function. Instead, the user sets the VOCZERO bit to
1 so that the TIP-RING voltage collapses to 0 V at the
rate programmed by the RAMP bit. Setting the
VOCZERO bit back to 0 returns the TIP-RING voltage
to its normal setting. With a software timer, the user can
automate the cadence of the wink function.
Figure 32illustrates the wink function.
Figure 32. Wink Function with Programmable Ramp Rate
Table 33. Register and RAM Locations used for Polarity Reversal
Parameter
Programmable Range
Register/RAM
Bits
Register/RAM
Mnemonic
Linefeed
LF[2:0]
LINEFEED
Polarity Reversal Status
Read only
POLREV
Wink Function
(Smooth transition to Voc=0V)
1 = Ramp to 0 V
0 = Return to previous VOC
VOCZERO
POLREV
Smooth Polarity Reversal Enable
0 = Disabled
1 = Enabled
PREN
POLREV
Smooth Polarity Reversal Ramp
Rate
0=1V/125 s
1=2V/125 s
RAMP
POLREV
V
TIP/RING (V)
0
-10
-20
-30
-40
-50
Time (ms)
50
40
30
20
10
60
70
80
0
2 V/125 s slope
set by RAMP bit
Set VOCZERO bit to 1
Set VOCZERO bit to 0
V
cm
V
ov
V
oc
V
TIP
V
BAT
V
RING