SI3232 datasheet(45/128 Pages) SILABS

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Si3232

Preliminary Rev. 0.96

4.12.1. Polarity Reversal

The Si3232 supports polarity reversal for message-

waiting functionality as well as various signaling modes.

The ramp rate can be programmed for a smooth

transition or an abrupt transition to accommodate

different application requirements. A wink function is

also provided for special equipment that responds to a

smooth ramp to VOC = 0 V. Table 27 illustrates the

modes.

An immediate reversal (hard reversal) of the line polarity

is achieved by setting the Linefeed register to the

opposite polarity. For example, a transition from

Forward Active mode to Reverse Active mode is

achieved by changing LF[2:0] from 001 to 101. Polarity

reversal can also be accommodated in the OHT and

ground-start modes. The POLREV bit is a read-only bit

that reflects whether the device is in polarity reversal

mode. A smooth polarity reversal is achieved by setting

the PREN bit to 1 and setting the RAMP bit to 0 or 1

depending on the desired ramp rate (see Table 27).

Polarity reversal is then accomplished by toggling the

linefeed register from forward to reverse modes as

desired.

A wink function is used to slowly ramp down the TIP-

RING voltage (VOC) to 1 followed by a return to the

original VOC value (set in the VOC RAM 0 location).

This scheme is used to light a message-waiting lamp in

certain handsets. To enable this function, no change to

the linefeed register is necessary. Instead, the user

must set the VOCZERO bit to 1 to cause the TIP-RING

voltage to collapse to 0 V at the rate programmed by the

RAMP bit. Setting the VOCZERO bit back to 0 causes

the TIP-RING voltage to return to its normal setting. A

software timer provided by the user can automate the

cadence of the wink function. Figure 23 illustrates the

wink function.

Table 27. Register and RAM Locations used for Polarity Reversal

Parameter

Programmable Range

Location

Linefeed

See Table 12

LF[2:0]

LINEFEED

Polarity Reversal Status

Read only

POLREV

Wink Function

(Smooth transition to Voc = 0 V)

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=1 V/125µs

1=2 V/125µs

RAMP

POLREV

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