Si3056
Si3018/19/10
These registers can help determine the following:
detection of another phone going off-hook by monitoring
the dc loop current. The LCS bits are decoded from
LCS2; so, both are available at the same time. The line
current sense transfer function is shown in Figure 19
and detailed in Table 16. The LCS and LCS2 bits report
loop current down to the minimum operating loop
current for the DAA. Below this threshold, the reported
value of loop current is unpredictable.
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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 or
off-hook.
Detect if enough loop current is available to operate.
When used in conjunction with the OPD bit, detect if
an overcurrent condition exists. (See "5.22.Overload
Detection" on page 35.)
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Table 16. Loop Current Transfer Function
5.8.1. Line Voltage Measurement
LCS[4:0]
Condition
The Si3056 device reports line voltage with the LVS[7:0]
bits (Register 29) in both on- and off-hook states with a
resolution of 1 V per bit. The accuracy of these bits is
approximately ±10%. Bits 0 through 6 of this register
indicate the value of the line voltage in 2s compliment
format. Bit 7 of this register indicates the polarity of the
tip/ring voltage.
If the INTE bit (Register 2) and the POLM bit (Register
3) are set, a hardware interrupt is generated on the
AOUT/INT pin when bit 7 of the LVS register changes
00000
Insufficient line current for normal
operation. Use the DOD bit (Register 19,
bit 1) to determine if a line is connected.
00100
11111
Minimum line current for normal operation.
Loop current is greater than 127 mA. An
overcurrent situation may exist.
5.9. Off-Hook
state. The edge-triggered interrupt is cleared by writing The communication system generates an off-hook
0 to the POLI bit (Register 4). The POLI bit is set each command by applying a logic 0 to the OFHK pin or by
time bit 7 of the LVS register changes state and must be setting the OH bit (Register 5, bit 0).The OFHK pin must
written to 0 to clear it.
be enabled by setting the OHE bit (Register 5, bit 1).
The polarity of the OFHK pin is selected by the OPOL
bit (Register 5, bit 4). With OFHK asserted, the system
is in an off-hook state.
The default state of the LVS register forces the LVS bits
to 0 when the line voltage is 3 V or less. The LVFD bit
(Register 31, bit 0) disables the force-to-zero function
and allows the LVS register to display non-zero values The off-hook state seizes the line for incoming/outgoing
of 3 V and below. This register might display calls and also can be used for pulse dialing. With OFHK
unpredictable values at line voltages between 0 to 2 V. deasserted, negligible dc current flows through the
At 0 V, the LVS register displays all 0s.
5.8.2. Loop Current Measurement
When the Si3056 is off-hook, the LCS2[7:0] and
LCS[4:0] bits measure loop current in 1.1 mA/bit and
3.3 mA/bit resolution respectively. These bits enable
hookswitch. When the OFHK pin is asserted, the
hookswitch transistor pair, Q1 and Q2, turn on. This
applies a termination impedance across TIP and RING
and causes dc loop current to flow. The termination
impedance has an ac and dc component.
Possible Overload
30
25
20
LCS
BITS
15
10
5
0
0
3.3 6.6 9.9 13.2 16.5 19.8 23.1 26.4 29.7 33 36.3 39.6 42.9 46.2 49.5 52.8
59.1 62.7
69.3 72.6 75.9
79.2 82.5 85.8 89.1 92.4 95.7 99 102.3
Loop 5C6.u1 rrent (m6A6)
127
Figure 19. Typical Loop Current LCS Transfer Function
26
Rev. 1.05
SILICON [ SILICON ]
