DS50PCI402 Datasheet, PDF (10/36 Pages) Texas Instruments – DS50PCI402 2.5 Gbps / 5.0 Gbps 4 Lane PCI Express Repeater with Equalization and De-Emphasis

Receiver Detection
The Rx detection process is a feature that can set the number
of active channels on the DS50PCI402. By sensing the pres-
ence of a valid PCIe load on the output, the channel can be
automatically enabled for operation. This allows the DS50P-
CI402 to configure inself to the proper lane width, whether it
is a 4-lane, 2-lane, or 1-lane PCIe link.
Automatic Rx Detection is enabled by a combination of
PRSNT# and ENRXDET inputs. When these inputs are set
low, Automatic Rx Detection is enabled, cycling of the
PRSNT# pin will reset the Rx detection circuitry, initiating a
new receiver detection sequence. Pulling the ENRXDET in-
put to logic 1, allows for manual control of the input termina-
tion.
The table below summarizes control pin and receiver detect
operation for the DS50PCI402.
TABLE 7. Receiver Detect Pins for A and B ports (LVCMOS inputs)
PRSNT# ENRXDET RXDETA/B
0
0
0
0
0
1
0
1
0
0
1
1
1
X
X
Input
Termination
>50KΩ to VDD
50Ω
>50KΩ to VDD
50Ω
>50KΩ to VDD
50Ω
>50KΩ to VDD
Termination sensed on
Output
Function
Hi - Z
PCIe Input
Automatic RXDET: Rx detection state
machine enabled. Outputs will test for the
presence of a receiver input every 12 msec
until detection occurs. Input termination
remains >50KΩ to VDD until receiver is
detected. Once receiver is detected, input
impedance to VDD is 50Ω.
Hi - Z
PCIe Input
Automatic RXDET: Rx detection state
machine enabled. Outputs will test for the
presence of a receiver input every 12 msec
for 600 msec and then stop. Input
termination remains >50KΩ to VDD until
receiver is detected. Once receiver is
detected, input impedance to VDD is 50Ω.
Restart detection if RXDETA/B is pulsed
low-high.
X
Manual RXDET: Rx detection state machine
disabled. Input termination >50KΩ.
Associated output channels in low power
idle mode.
X
Manual RXDET: Rx detection state machine
disabled. Input termination 50Ω. Associated
output channels set to active.
X
Power down mode: Input termination
>50KΩ. Associated output channels off. Part
in power saving mode. PRSNT# should be
held high for a minimum of 5 us to ensure
complete analog power down. The
Automatic RXDET functionality will be re-
initialized on the falling edge of PRSNT#.
RX Detect: Range of Operation
The Rx detection process used in the DS50PCI402 is de-
signed to be fully compliant with the PCIe 2.0 base specifica-
tion. The receiver detection circuitry will accurately detect a
receiver when both conditions listed below are true:
• DS50PCI402 within Recommended Operating Range for
Temperature and Supply Voltage
• For receiver Z_RX-DC = 40 (min) to 60 (max) Ohms
Note: To ensure robust system operation, the DS50PCI402
will only signal a valid receiver detection if both halves of the
differential output pair detect a proper 40 - 60 Ohm receiver
impedance. If the receiver detection circuitry senses a load
impedance greater than Z_RX-DC on either trace of a differential
pair, it will be interpreted as no termination load present (i.e.
the corresponding DS50PCI402 input termination will remain
High-Z).
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