px1011a NXP Semiconductors, px1011a Datasheet - Page 9

• Manufacturer Part Number: px1011a
• Description: Px1011a/px1012a Pci Express Stand-alone X1 Phy
• Manufacturer: NXP Semiconductors

Philips Semiconductors
PX1011A_PX1012A_2
Product data sheet
8.2 Transmitting data
8.3 Clocking
8.4 Reset
The de-serializer or Serial-to-Parallel converter (S2P) de-serializes this data into 10-bits
parallel data.
Since the S2P has no knowledge about the data, the word alignment is still random. This
is fixed in the digital domain by the PCS block. It first detects a 10-bit comma character
(K28.5) from the random data stream and aligns the bits. Then it converts the 10-bit raw
data into 8-bit words using 8b/10b decoding. An elastic buffer and FIFO brings the
resulting data to the right clock domain, which is the RX source synchronous clock
domain.
When the PHY transmits, it receives 8-bit data from the MAC. This data is encoded using
an 8b/10b encoding algorithm. The 2 bits overhead of the 8b/10b encoding ensures the
serial data will be DC-balanced and has a sufficient 0-to-1 and 1-to-0 transition density for
clock recovery at the receiver side.
The serializer or Parallel-to-Serial converter (P2S) serializes the 10 bits data into serial
data streams. These data streams are latched into the transmitter, where they are
converted into small amplitude differential signals. The transmitter has built-in
de-emphasis for a larger eye opening at the receiver side.
The PLL has a sufficiently high bandwidth to handle a 100 MHz reference clock with a
30 kHz to 33 kHz spread spectrum.
There are three clock signals used by the PX1011A/1012A:
The PHY must be held in reset until power and REFCLK are stable. It takes the PHY
64 s maximum to stabilize its internal clocks. RXCLK frequency is the same as REFCLK
frequency, 100 MHz, during this time. The PHY de-asserts PHYSTATUS when internal
clocks are stable.
The PIPE specification recommends that while RESET_N is asserted, the MAC should
have RXDET_LOOPB de-asserted, TXIDLE asserted, TXCOMP de-asserted, RXPOL
de-asserted and power state P1. The MAC can also assert a reset if it receives a physical
layer reset packet.
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REFCLK is a 100 MHz external reference clock that the PHY uses to generate the
250 MHz data clock and the internal bit rate clock. This clock may have
30 kHz to 33 kHz spread spectrum modulation.
TXCLK is a reference clock that the PHY uses to clock the TXDATA and command.
This source synchronous clock is provided by the MAC. The PHY expects that the
rising edge of TXCLK is centered to the data. The TXCLK has to be synchronous with
RXCLK.
RXCLK is a source synchronous clock provided by the PHY. The RXDATA and status
signals are synchronous to this clock. The PHY aligns the rising edge of RXCLK to
the center of the data. RXCLK may be used by the MAC to clock its internal logic.
Rev. 02 — 18 May 2006
PX1011A/PX1012A
PCI Express stand-alone X1 PHY
© Koninklijke Philips Electronics N.V. 2006. All rights reserved.
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