AD8155 查看數據表（PDF） - Analog Devices
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AD8155 Datasheet PDF : 36 Pages
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AD8155
LOSS OF SIGNAL (LOS)
The serial control interface allows access to the AD8155 loss of
signal features (LOS is not available in pin control mode). Each
receiver includes a low power, loss-of-signal detector. The loss-
of-signal circuit monitors the received data stream and generates a
system interrupt when the received signal power falls below a
fixed threshold. The threshold is 50 mV p-p diff, referred to the
input pins. The LOS circuit monitors the equalized receive wave-
form and integrates the rms power of the equalized waveform
over a selectable interval of either 2 ns or 10 ns. The detectors are
enabled on a per-port basis with Bit 0 of the RXA/B/C LOS control
registers (0x51, 0x91, 0xD1).
By default, when the receiver detects an LOS event, it squelches
its associated transmitter, lowering the output current to
submicroamps. This prevents the high gain, wide bandwidth
signal path from turning low level system noise on an undriven
input pair into a source of hostile crosstalk at the transmitter.
The squelch feature can be disabled with Bit 3 of the global
squelch control register (0x04).
The LOS_INT pin evaluates a logical OR of all LOS status
register bits for all enabled receivers (LOS status registers are
located at 0x45, 0x85, and 0xC5). The upper two bits in the
RXA, RXB, and RXC LOS status registers are sticky, whereas
the two LSBs are continuously updated to indicate the instantan-
eous status of LOS for an enabled receiver. The sticky bits are
cleared by writing 0 to the RXA, RXB, and RXC LOS status
registers. The LOS_INT pin remains high after an LOS event
until all sticky registers are cleared and all active status registers
(for example, Bits[1:0]) read 0. The LOS_INT pin requires that
an initialization sequence be enabled (see the Applications
Information section).
The LOS_INT pin can be used to generate an interrupt for the
system control software. In a standard implementation, when
LOS_INT goes high, the system software registers the interrupt
and polls the RXA, RXB, and RXC LOS status registers to
determine which input lost signal and whether the signal has
been restored.
Table 14. Global Loss-of-Signal Squelch Control Register
Address Default Register Name
0x04
0x0F
Global Squelch Ctrl
Table 15. Port-Level Loss-of-Signal Control Registers
Address Port
Default
Register Name
0x51
0x91
Port A
Port B
0x05
0x05
RX[A/B/C] LOS
control
0xD1
Port C 0x05
Table 16. Port-Level Loss-of-Signal Status Registers
Address Port
Default
Register Name
0x45
Port A Read only
0x85
0xC5
Port B
Port C
Write 0 to clear RX[A/B/C] LOS
status
Bit Bit Name
7:4 Reserved
3
GSQLCH_ENB
2:0 Reserved
Functionality Description
Set to 0
0: LOS auto squelch disabled
1: LOS auto squelch enabled
Set to 1
Bit Bit Name
7:3 Reserved
2
LOS_FILT
1
Reserved
0
LOS_ENB
Functionality Description
Set to 0
0: LOS filter time constant = 2 ns
1: LOS filter time constant = 10 ns
Set to 0
0: LOS disabled
1: LOS enabled
Bit Bit Name
Functionality Description
7:6 Reserved
5:4 LOS[A/B/C][1:0] 00: LOS event has not occurred.
sticky
01: LOS event has occurred on Lane 0.
10: LOS event has occurred on Lane 1.
11: LOS event has occurred on both lanes.
Read only; write 0 to clear.
3:2 Reserved
1:0 LOS[A/B/C][1:0] 00: active signals on both lanes.
active
01: inactive signal on Lane 0.
10: inactive signal on Lane 1.
11: inactive signals on both lanes.
Read only.
Rev. 0 | Page 20 of 36
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