AM79C864AKCW AMD [Advanced Micro Devices], AM79C864AKCW Datasheet - Page 41

• Manufacturer Part Number: AM79C864AKCW
• Description: Physical Layer Controller With Scrambler (PLC-S)
• Manufacturer: AMD [Advanced Micro Devices]

detects a fragment, i.e., a frame in which Idle symbols
appears before the ending delimiter, then it changes the
previous symbol pair to Idles. After passing through Re-
peat Filters in other stations, the fragment will eventually
be completely converted to Idles.
The PLC-S includes the symbol pair wide implementa-
tion of the Repeat Filter as defined in the FDDI PHY
document.
Data Stream Generator
The Data Stream Generator block uses a multiplexer for
the purpose of generating a symbol pair at the request of
the PCM via an internal signal bus LS_REQ (or external
through control when the PCM is in the MAINT state by
using the MAINT_LS bits in the PLC_CNTRL_B regis-
ter), the Repeat Filter via an internal signal RF-CNTRL
(1_0), or transmitting the symbol pair from TX 9–0. The
DATA_STRM(9–0) is an internal bus that comes from
the Data Stream Generator to the encoder block.
The Data Stream Generator also latches the data each
BCLK cycle. This is done for the GOBBLE_BYTE func-
tion of the Repeat Filter (see above) which requires that
the data be delayed for one clock cycle.
Data Path Muxes
The Receive Data Path and Transmit Data Path of the
PLC-S include six multiplexers (MUXes) for the pur-
pose of altering the normal flow of data through the chip
(see chip block diagram). Reasons for altering the data
paths are for physical connection insertion and removal
and for testing and diagnostics. All receive and transmit
data paths internal to the PLC-S are ten bits (two
symbols) wide.
EB Local Loopback Mux
In normal operating mode, the EB Local Loopback MUX
puts the data held in the Receive Data Input latch to the
input of Framer.
When the EB_LOC_LOOP bit in the PLC_CNTRL_A
register is set or when the built-in self test is running, the
MUX loops back the data in the Transmit Data Output
latch onto the receive data path just after the Receive
Data Input latch (i.e., to the input of Framer). This cre-
ates a path whereby data from a MAC device can trav-
erse the entire transmit and receive data paths of the
PLC-SS (excluding the scrambler and the descrambler)
and be returned to the MAC device. The built-in self test
uses this loopback along with the Remote Loopback to
create a loop which covers all of the transmit data path
and receive data path.
Cipher Loopback MUX
In normal operating mode, the Cipher Lookback MUX
puts the data from PDR to the input of the descrambler
block of PLC-SS and the data from the scrambler block
of PLC-SS to PDT.
P R E L I M I N A R Y
Am79C864A
When the CIPHER_LPBCK bit in the PLC_CNTRL_C
register is set, the MUX loops back the output of the
descrambler to the input of the scrambler. This creates a
path whereby data from a MAC device can traverse the
entire transmit and receive data paths of the PLC-SS
(including the scrambler and the descrambler) and be
returned to the MAC device.
LM Local Loopback MUX
In normal operating mode, the LM Local Loopback MUX
puts the output of Elasticity buffer/smoother block to the
input of Decoder block.
When the LM_LOC_LOOP bit in the PLC_CNTRL_A
register is set or when the built-in self test is running, the
MUX loops back the data in the Transmit Data Output
latch onto the receive data path just after the Elasticity
buffer. This differs from the EB_LOC_LOOP in that the
Framer and Elasticity Buffer are bypassed.
Bypass MUX
In normal operating mode, the Bypass MUX sends the
data output by the Decoder to the Receive Data Output
latch.
When the SC_BYPASS bit in the PLC_CNTRL_A regis-
ter is set while the PCM is in the MAINT state, or when
the CONFIG_CNTRL bit is set in the PLC_CNTRL_B
register, or when the PCI is in the REMOVED, IN-
SERT_SCRUB, or REMOVE_SCRUB state, the output
of the BYPASS MUX is put to the Transmit Data Input
Latch onto the receive data path. On reset this
BYPASS_MUX will be in effect and will put the Transmit
Data Input Latch onto the receive data path.
Remote Loopback MUX
In normal operating mode, the Remote Loopback MUX
puts the data held in the Transmit Data Input latch onto
the transmit data path of the PLC-SS.
When
EB_LOC_LOOP, LM_LOC_LOOP and CIPHER_
LPBCK bits are not set) or when the BIST is running,
this MUX loops back the data from the Decoder onto the
transmit data path and is latched at this point. This cre-
ates a path whereby data from the PDR can traverse the
entire receive and transmit data paths of the PLC-S and
be transmitted by PDT. BIST uses this loopback along
with the Local Loopback to create a loop which also cov-
ers all of the receive data path and the transmit data
path.
Scrub MUX
The Scrub MUX selects its input from either constant
Idle symbol pairs or the output of the BYPASS_MUX.
When the REQ_SCRUB bit in the PLC_CNTRL_A reg-
ister is set while the PCM is in the MAINT state, or when
CONFIG_CNTRL bits is set in the PLC_CNTRL_B
the
SC_REM_LOOP
bit
is
set
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