2–158
Altera Corporation
Stratix II GX Device Handbook, Volume 2
October 2007
Native Modes
An additional status port,
rx_pipedatavalid
, indicates that the data
on the
rx_dataout
port is valid. This signal is equivalent to the
rx_syncstatus
port. The
rx_pipedatavalid
port operates in
parallel with the
pipestatus
signal.
Receiver Detect
The receiver detect circuitry is available for PCI Express applications. The
receiver detect circuitry is only available in the P1 power state and is set
through the
tx_detectrxloopback
port and requires a 125 MHz
fixedclk
signal. In the P1 power state, a high on
tx_detectrxloopback
port triggers the receiver detect circuitry to
alter the transmitter buffer common mode voltage. The sudden change in
common mode voltage effectively appears as a step voltage at the serial
link. If a receiver (that complies to PCI-Express input impedance
requirements) is present at the far end, the time constant of the step
voltage is higher. If a receiver is not present or powered down, the time
constant of the step voltage is lower. The receiver detect circuitry snoops
the serial line (
tx_dataout
) for the time constant of the step voltage to
detect the presence of the receiver at the far end.
Upon receiver detect, the pipestatus port indicates if a receiver is detected
or not. There is some latency after asserting the
tx_detectrxloopback
signal, before the receiver detection is indicated. The
tx_forceelecidle
port must be asserted at least 10 parallel clock
cycles prior to the
tx_detectrxloopback
to ensure that the
transmitter buffer is tri-stated.
Beacon Transmission
The beacon is an optional 30 kHz to 500 MHz in-band signal that wakes
the receiver from a P2 power state. This signal is optional, and the
Stratix II GX device does not have dedicated beacon transmission
circuitry. The Stratix II GX device supports the transmission of the beacon
signal through a 10-bit encoded code word that has a five 1’s pulse (for
example, K28.5).
Because the beacon signal is a pulse that ranges from 2 ns to 500 ns,
sending out a K28.5 at 2.5 Gbps meets the lower requirement with its five
1’s pulse. (Though other 8B/10B code groups might meet the beacon
requirement, this document uses the K28.5 control code group as the
beacon signal.) The beacon transmission takes place only in the P2 power
state. The
tx_forceelecidle
port controls when the transmitter is in
Electrical Idle or not. This port must be deasserted in order to transmit the
K28.5 code group.
Содержание Stratix II GX
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