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SI3021 Datasheet(PDF) 25 Page - List of Unclassifed Manufacturers |
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SI3021 Datasheet(HTML) 25 Page - List of Unclassifed Manufacturers |
25 / 54 page Si3035 Rev. 1.2 25 AOUT signal can be set to –20 dB, –26 dB, –32 dB, or mute. The receive portion of the AOUT signal can be set to 0 dB, –6 dB, –12 dB, or mute. Figure 17 on page 17 illustrates a recommended application circuit. In the configuration shown, the LM386 provides a gain of 26 dB. Additional gain adjustments may be made by varying the voltage divider created by R1 and R3 of Figure 17. On-Hook Line Monitor The Si3035 allows the user to detect line activity when the device is in an on-hook state. When the system is on-hook, the line data can be passed to the DSP across the serial port while drawing a small amount of DC current from the line. This feature is similar to the passing of line information (such as caller ID), while on-hook, following a ring signal detection. To activate this feature, set the ONHM bit in Register 5. The on-hook line monitor can also be used to detect whether a phone line is physically connected to the Si3012 and associated circuitry. When the on-hook line monitor is activated (if no line is connected), the output of SDO will move towards a negative full scale value (–32768). The value is guaranteed to be at least 89% of negative full scale. If a line is present while in on-hook line monitor mode, SDO will have a near zero value. The designer must allow for the group delay of the receive filter (12/Fs) before making a decision. Loop Current Monitor When the system is in an off-hook state, the LCS bits of Register 12 indicate the approximate amount of DC loop current that is flowing in the loop. The LCS is a 4-bit value ranging from zero to fifteen. Each unit represents approximately 6 mA of loop current from LCS codes 1–14. The typical LCS transfer function is shown in Figure 24. Figure 24. Typical LCS Transfer Function An LCS value of zero means the loop current is less than required for normal operation and the system should be on-hook. Typically, an LCS value of 15 means the loop current is greater than 155 mA. The LCS detector has a built-in hysteresis of 2 mA of current. This allows for a stable LCS value when the loop current is near a transition level. The LCS value is a rough approximation of the loop current, and the designer is advised to use this value in a relative means rather than an absolute value. This feature enables the host processor to detect if an additional line has “picked up” while the modem is transferring information. In the case of a second phone going off-hook, the loop current falls approximately 50% and is reflected in the value of the LCS bits. Multiple Device Support The Si3035 supports the operation of up to seven additional devices on a single serial interface. Figure 25 on page 27 shows the typical connection of the Si3035 and one additional serial voice codec (Si3000). The Si3035 must be the master in this configuration. The secondary codec should be configured as a slave device with SCLK and FSYNC as inputs. On power up, the Si3035 master will be unaware of the additional codec on the serial bus. The FC/RGDT pin is an input, operating as the hardware control for secondary frames. The RGDT/FSD pin is an output, operating as the active low ring detection signal. It is recommended that the master device be programmed for master/slave mode prior to enabling the ISOcap, because a ring signal would cause a false transition to the slave device’s FSYNC. Register 14 provides the necessary control bits to configure the Si3035 for master/slave operation. Bit 0 (DCE) sets the Si3035 in master/slave mode, also referred to as daisy-chain mode. When the DCE bit is set, the FC/RGDT pin becomes the ring detect output and the RGDT/FSD pin becomes the frame sync delay output. Bits 7:5 (NSLV2:NSLV0) set the number of slaves to be supported on the serial bus. For each slave, the Si3035 will generate a FSYNC to the DSP. In daisy-chain mode, the polarity of the ring signal can be controlled by bit 1 (RPOL). When RPOL = 1, the ring detect signal (now output on the FC/RGDT pin) is active high. The Si3035 supports a variety of codecs (e.g., Si3000) as well as additional Si3035s. The type of slave codec(s) used is set by bits 4:3 (SSEL1:SSEL0). These bits determine the type of signalling used in the LSB of SDO. This assists the DSP in isolating which data stream is the master and which is the slave. If the LSB is used for 0 5 10 15 LC S BIT 0 6 12 18 24 30 36 42 48 54 60 66 72 155 78 84 90 96 Loop C urrent (m A) |
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