Si3220/Si3225
Linefeed Operation States
The linefeed interface includes eight different operating more details. The register and RAM locations used for
states as shown in Table 17. The linefeed register programming the linefeed parameters are provided in
settings (LF[2:0], linefeed register) are also listed. The Table 18. See “Loop Voltage and Current Monitoring”
open state is the default condition in the absence of any and "Power Monitoring and Power Fault Detection" on
pre-loaded register settings. The device may also page 35, and "Power Dissipation Considerations" on
automatically enter the open state if excess power page 39 for detailed descriptions and register/RAM
consumption is detected in the Si3200. See "Power locations for these functions.
Monitoring and Power Fault Detection" on page 35 for
Table 17. Linefeed States
Open (LF[2:0] = 000).
The Si3200 output is high-impedance. This mode can be used in the presence of line fault conditions and to
generate open-switch intervals (OSIs). The device can also automatically enter the Open state if excess power
consumption is detected in the Si3200 or in the discrete bipolar transistors.
Forward Active (LF[2:0] = 001).
Linefeed is active, but audio paths are powered down until an off-hook condition is detected. The Si3220 and
Si3225 automatically enter a low-power state to reduce power consumption during on-hook standby periods.
Forward On-Hook Transmission (LF[2:0] = 010).
Provides data transmission during an on-hook loop condition (e.g., transmitting FSK caller ID information
between ringing bursts).
Tip Open (LF[2:0] = 011).
Sets the portion of the linefeed interface connected to the TIP side of the subscriber loop to high-impedance
and provides an active linefeed on the RING side of the loop for ground-start operation.
Ringing (LF[2:0] = 100).
Drives programmable ringing waveforms onto the subscriber loop (Si3220) or switches in a centralized ringing
generator by driving an external relay (Si3225).
Reverse Active (LF[2:0] = 101).
Linefeed circuitry is active, but audio paths are powered down until an off-hook condition is detected. The
Si3220 and Si3225 automatically enter a low-power state to reduce power consumption during on-hook
standby periods.
Reverse On-Hook Transmission (LF[2:0] = 110).
Provide data transmission during an on-hook loop condition.
Ring Open (LF[2:0] = 111).
Sets the portion of the linefeed interface connected to the RING side of the subscriber loop to high impedance
and provides an active linefeed on the TIP side of the loop for ground start operation.
Rev. 1.0
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SILICONIMAGE [ Silicon image ]
