SI3056-KS Datasheet(数据表) 26 Page - Silicon Laboratories

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zoom inzoom out 26 pageSi3056Si3018/19/1026Rev. 1.05These registers can help determine the following:When on-hook, detect if a line is connected.When on-hook, detect if a parallel phone is off-hook.When off-hook, detect if a parallel phone goes on oroff-hook.Detect if enough loop current is available to operate.When used in conjunction with the OPD bit, detect ifan overcurrent condition exists. (See 5.22.OverloadDetection on page 35.)5.8.1. Line Voltage MeasurementThe Si3056 device reports line voltage with the LVS[7:0]bits (Register 29) in both on- and off-hook states with aresolution of 1 V per bit. The accuracy of these bits isapproximately ±10%. Bits 0 through 6 of this registerindicate the value of the line voltage in 2s complimentformat. Bit 7 of this register indicates the polarity of thetip/ring voltage.If the INTE bit (Register 2) and the POLM bit (Register3) are set, a hardware interrupt is generated on theAOUT/INT pin when bit 7 of the LVS register changesstate. The edge-triggered interrupt is cleared by writing0 to the POLI bit (Register 4). The POLI bit is set eachtime bit 7 of the LVS register changes state and must bewritten to 0 to clear it.The default state of the LVS register forces the LVS bitsto 0 when the line voltage is 3 V or less. The LVFD bit(Register 31, bit 0) disables the force-to-zero functionand allows the LVS register to display non-zero valuesof 3 V and below. This register might displayunpredictable values at line voltages between 0 to 2 V.At 0 V, the LVS register displays all 0s.5.8.2. Loop Current MeasurementWhen the Si3056 is off-hook, the LCS2[7:0] andLCS[4:0] bits measure loop current in 1.1 mA/bit and3.3 mA/bit resolution respectively. These bits enabledetection of another phone going off-hook by monitoringthe dc loop current. The LCS bits are decoded fromLCS2; so, both are available at the same time. The linecurrent sense transfer function is shown in Figure 19and detailed in Table 16. The LCS and LCS2 bits reportloop current down to the minimum operating loopcurrent for the DAA. Below this threshold, the reportedvalue of loop current is unpredictable.5.9. Off-HookThe communication system generates an off-hookcommand by applying a logic 0 to the OFHK pin or bysetting the OH bit (Register 5, bit 0).The OFHK pin mustbe enabled by setting the OHE bit (Register 5, bit 1).The polarity of the OFHK pin is selected by the OPOLbit (Register 5, bit 4). With OFHK asserted, the systemis in an off-hook state.The off-hook state seizes the line for incoming/outgoingcalls and also can be used for pulse dialing. With OFHKdeasserted, negligible dc current flows through thehookswitch. When the OFHK pin is asserted, thehookswitch transistor pair, Q1 and Q2, turn on. Thisapplies a termination impedance across TIP and RINGand causes dc loop current to flow. The terminationimpedance has an ac and dc component.Figure 19. Typical Loop Current LCS Transfer FunctionTable 16. Loop Current Transfer FunctionLCS[4:0]Condition00000Insufficientlinecurrentfornormaloperation. Use the DOD bit (Register 19,bit 1) to determine if a line is connected.00100Minimum line current for normal operation.11111Loop current is greater than 127 mA. Anovercurrent situation may exist.03.36.69.9 13.2 16.5 19.8 23.1 26.43336.3 39.6 42.9 46.2 49.5 52.8 56.1 59.1 62.7 6669.3 72.6 75.9 79.212782.5 85.8 89.1 92.4 95.7 99 102.3Loop Current (mA)LCSBITS29.7051015202530Possible Overload