Si3050 datasheet(37/128 Pages) SILABS

37 / 128 page

Si3050 + Si3011/18/19

Rev. 1.5

f. Set the OH bit to return to an off-hook state.

Immediately after returning to an off-hook state,

the off-hook counter must be allowed to expire.

This allows the line voltage to settle before

transmitting or receiving data. After 8 ms normal

data transmission and reception can begin. If a

non-compliant parallel device is present, then a

reply tone is not sent by the host tone generator

and the CO does not send the CID data. If all

devices on the line are Type II CID compliant,

then the host must mute its upstream data output

to avoid the propagation of its reply tone and the

subsequent CID data. When muting its upstream

data output, the host processor should return an

acknowledgement (ACK) tone to the CO

requesting transmission of CID data.

3. The CO then responds with CID data after receiving

the CID data, the host processor unmutes the

upstream data output and continues with normal

operation.

4. The muting of the upstream data path by the host

processor mutes the handset in a telephone

application so the user cannot hear the

acknowledgement tone and CID data being sent.

5. The CALD and the RCALD bits can be cleared to

re-enable the automatic calibrations when going

off-hook. The FOH[1:0] bits also can be programmed

to 01 to restore the default off-hook counter time.

Because of the nature of the low-power ADC, the data

presented on DTX can have up to a 10% dc offset. The

caller ID decoder must either use a high-pass or a

band-pass filter to accurately retrieve the caller ID data.

Figure 26. Implementing Type II Caller ID on the Si3050+Si3011/19

5.26. Overload Detection

The Si3050 can be programmed to detect an overload

condition that exceeds the normal operating power

range of the DAA circuit. To use the overload detection

feature, the following steps should be followed:

1. Set the OH bit (Register 5, bit 0) to go off-hook, and

wait 25 ms to allow line transients to settle.

2. Enable overload detection by then setting the OPE

bit (Register 17, bit 3).

If the DAA senses an overload situation it automatically

presents an 800  impedance to the line to reduce the

hookswitch current. At this time, the DAA also sets the

OPD bit (Register 19, bit 0) to indicate that an overload

condition exists. The line current detector within the

DAA has a threshold that is dependent on the ILIM bit

(Register 26). When ILIM = 0, the overload detection

threshold equals 160 mA. When ILIM = 1, the overload

detection threshold equals 60 mA. The OPE bit should

always be cleared before going off-hook.

Notes:

1. The off-hook counter and calibrations prevent transmission or reception of data for 402.75 ms (default) for the line

voltage to settle.

2. The caller alert signal (CAS) tone transmits from the CO to signal an incoming call.

3. The device is taken on-hook to read the line voltage in the LVS bits to detect parallel handsets. In this mode, no data is

transmitted on the DTX pin.

4. When the device returns off-hook, the normal off-hook counter is reduced to 8 ms. If the CALD and RCALD bits are set,

then the automatic calibrations are not performed.

5. After allowing the off-hook counter to expire (8 ms), normal transmission and reception can continue. If CID data

reception is required, send the appropriate signal to the CO at this time.

LINE

FOH[1] Bit

RCALD Bit

CALD Bit

OH Bit

FOH[0] Bit

On-Hook

Off-Hook Counter

and Calibration

(402.75 ms nominally)

Off-Hook

CAS Tone

Received

On-Hook

Off-Hook Counter

(8 ms)

Off-Hook

Ack

Si3050 Datasheet(PDF) 37 Page - Silicon Laboratories

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