Si3050 + Si3011/18/19
Rev. 1.5
37
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
1
23
4
5
OH Bit
FOH[0] Bit
On-Hook
Off-H ook C ounter
and C alibration
(402.75 ms nominally)
Of f -Hook
CA S Tone
Rec eiv ed
On-Hook
Off-Hook Counter
(8 ms)
Of f -Hook
A ck