AM7968-125DKC Advanced Micro Devices, AM7968-125DKC Datasheet - Page 21

• Manufacturer Part Number: AM7968-125DKC
• Description: TAXIchip Integrated Circuits(Transparent Asynchronous Xmitter-Receiver Interface)
• Manufacturer: Advanced Micro Devices

Am7969 Receiver Functional Block
Description
(Refer to page 1)
Crystal Oscillator/Clock Generator
The data recovery PLL in the Am7969 must be supplied
with a reference frequency at the expected byte rate of
the data to be recovered. The source of this frequency
can either be the built-in Crystal Oscillator, or an exter-
nal clock signal applied through the X
ence frequency source is then multiplied by ten (8-bit
mode), eleven (9-bit mode) or twelve (10-bit mode) us-
ing an internal PLL.
Media Interface
SERIN+, SERIN– inputs are to be driven by differential
ECL voltages, referenced to +5 V. Serial data at these
inputs will serve as the reference for PLL tracking.
PLL Clock Generator
A PLL Clock recovery loop follows the incoming data
and allows the encoded clock and data stream to be de-
coded into a separated clock and data pattern. It uses
the crystal oscillator and clock generator to predict the
expected frequency of data and will track jittered data
with a characteristically small offset frequency.
Shifter
The Shifter is serially loaded from the Media Interface,
using the bit clock generated by PLL.
Byte Sync Logic
The incoming data stream is a continuous stream of
data bits, without any significant signal which denotes
byte boundaries. This logic will continuously monitor the
data stream, and upon discovering the reserved code
used for Am7969 Receiver Sync, will initialize a
synchronous counter which counts bits, and indicates
byte boundaries.
The logic signal that times data transfers from the Shif-
ter to the Decoder Latch is buffered and sent to the CLK
output. CLK output from the Receiver is not suitable as a
frequency source for another TAXI Transmitter or Re-
ceiver. It is intended to be used by the host system as a
clock synchronous with the received data. This output is
synchronous with the byte boundary and is synchronous
with the Receiver’s internal byte clock.
Byte Sync Logic is responsible for generating the inter-
nal strobe signals for Parallel Output Latches. It also
generates the IGM (I-Got-Mine) signal in Test mode
1
pin. The refer-
Am7968/Am7969
when the first byte after a Sync symbol is transferred.
Parallel outputs are made on a byte boundary, after
CNB falls, or when Sync is detected.
The I-Got-Mine ( IGM ) signal will fall when the first half of
a Sync is detected in the Shifter or when CNB goes
LOW. It will remain LOW until the first half of a non-Sync
byte is detected in the Shifter, whereupon it will rise (as-
suming that the CNB input is HIGH). A continuous
stream of normal data or command bytes will cause IGM
to go HIGH and remain HIGH. A continuous stream of
Sync’s will cause IGM to stay LOW. IGM will go HIGH
during the byte before data appears at the output. This
feature could be used to generate an early warning of in-
coming data.
Decoder Latch
Data is loaded from the Shifter to this latch at each
symbol/byte boundary. It serves as the input to the
Data Decoder.
Data Decoder
Decodes ten, eleven, or twelve data inputs into twelve
outputs. In 8-bit mode, data is decoded into either an
8-bit Data pattern or a 4-bit Command pattern. In 9-bit
mode, data is decoded into either a 9-bit Data pattern or
a 3-bit Command pattern. In 10-bit mode, data is de-
coded into either a 10-bit Data pattern or a 2-bit Com-
mand pattern.
The decoder separates Data symbols from Command
symbols, and causes the appropriate strobe output to
be asserted.
Parallel Output Latch
Output Latch will be clocked by the byte clock, and will
reflect the most recent data on the link. Any Data pattern
will be latched to the Data outputs and will not affect the
status of the Command outputs. Likewise, any Com-
mand pattern will be latched to the Command outputs
without affecting the state of the Data outputs.
Any data transfer, either Data or Command will be syn-
chronous with an appropriate output strobe. However,
there will be CSTRBs when there is no active data on the
link, since Sync is a valid Command code.
Any pattern which does not decode to a valid Command
or Data pattern is flagged as a violation. The output of
the decoder during these violations is indeterminate and
will result in either a CSTRB or DSTRB output when the
indeterminate pattern is transferred to the output latch.
AMD
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