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DP83847ALQA56A

Part # DP83847ALQA56A
Description IC ETHERNET TRANSCEIVER 56WQFN
Category IC
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National Semiconductor Corp
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Technical Document


DISCLAIMER: The information provided herein is solely for informational purposes. Customers must be aware of the suitability of this product for their application, and consider that variable factors such as Manufacturer, Product Category, Date Codes, Pictures and Descriptions may differ from available inventory.

15 www.national.com
DP83847
3.0 Functional Description
3.1 802.3u MII
The DP83847 incorporates the Media Independent Inter-
face (MII) as specified in Clause 22 of the IEEE 802.3u
standard. This interface may be used to connect PHY
devices to a MAC in 10/100 Mb/s systems. This section
describes both the serial MII management interface as well
as the nibble wide MII data interface.
The serial management interface of the MII allows for the
configuration and control of multiple PHY devices, gather-
ing of status, error information, and the determination of the
type and capabilities of the attached PHY(s).
The nibble wide MII data interface consists of a receive bus
and a transmit bus each with control signals to facilitate
data transfer between the PHY and the upper layer (MAC).
3.1.1 Serial Management Register Access
The serial management MII specification defines a set of
thirty-two 16-bit status and control registers that are acces-
sible through the management interface pins MDC and
MDIO. The DP83847 implements all the required MII regis-
ters as well as several optional registers. These registers
are fully described in Section 4.0. A description of the serial
management access protocol follows.
3.1.2 Serial Management Access Protocol
The serial control interface consists of two pins, Manage-
ment Data Clock (MDC) and Management Data Input/Out-
put (MDIO). MDC has a maximum clock rate of 25 MHz
and no minimum rate. The MDIO line is bi-directional and
may be shared by up to 32 devices. The MDIO frame for-
mat is shown below in Table 4: Typical MDIO Frame For-
mat.
The MDIO pin requires a pull-up resistor (1.5 k) which,
during IDLE and turnaround, will pull MDIO high. In order to
initialize the MDIO interface, the station management entity
sends a sequence of 32 contiguous logic ones on MDIO to
provide the DP83847 with a sequence that can be used to
establish synchronization. This preamble may be gener-
ated either by driving MDIO high for 32 consecutive MDC
clock cycles, or by simply allowing the MDIO pull-up resis-
tor to pull the MDIO pin high during which time 32 MDC
clock cycles are provided. In addition 32 MDC clock cycles
should be used to re-sync the device if an invalid start,
opcode, or turnaround bit is detected.
The DP83847 waits until it has received this preamble
sequence before responding to any other transaction.
Once the DP83847 serial management port has been ini-
tialized no further preamble sequencing is required until
after a power-on/reset, invalid Start, invalid Opcode, or
invalid turnaround bit has occurred.
The Start code is indicated by a <01> pattern. This assures
the MDIO line transitions from the default idle line state.
Turnaround is defined as an idle bit time inserted between
the Register Address field and the Data field. To avoid con-
tention during a read transaction, no device shall actively
drive the MDIO signal during the first bit of Turnaround.
The addressed DP83847 drives the MDIO with a zero for
the second bit of turnaround and follows this with the
required data. Figure 2 shows the timing relationship
between MDC and the MDIO as driven/received by the Sta-
tion (STA) and the DP83847 (PHY) for a typical register
read access.
For write transactions, the station management entity
writes data to the addressed DP83847 thus eliminating the
requirement for MDIO Turnaround. The Turnaround time is
filled by the management entity by inserting <10>. Figure 3
shows the timing relationship for a typical MII register write
access.
3.1.3 Serial Management Preamble Suppression
The DP83847 supports a Preamble Suppression mode as
indicated by a one in bit 6 of the Basic Mode Status Regis-
ter (BMSR, address 01h.) If the station management entity
(i.e. MAC or other management controller) determines that
all PHYs in the system support Preamble Suppression by
Table 4. Typical MDIO Frame Format
MII Management
Serial Protocol
<idle><start><op code><device addr><reg addr><turnaround><data><idle>
Read Operation <idle><01><10><AAAAA><RRRRR><Z0><xxxx xxxx xxxx xxxx><idle>
Write Operation <idle><01><01><AAAAA><RRRRR><10><xxxx xxxx xxxx xxxx><idle>
Figure 2. Typical MDC/MDIO Read Operation
MDC
MDIO
00011 110000000
(STA)
Idle Start
Opcode
(Read)
PHY Address
(PHYAD = 0Ch)
Register Address
(00h = BMCR)
TA
Register Data
Z
MDIO
(PHY)
Z
Z
Z
0 0 011000100000000
Z
Idle
Z
Z
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DP83847
returning a one in this bit, then the station management
entity need not generate preamble for each management
transaction.
The DP83847 requires a single initialization sequence of
32 bits of preamble following hardware/software reset. This
requirement is generally met by the mandatory pull-up
resistor on MDIO in conjunction with a continuous MDC, or
the management access made to determine whether Pre-
amble Suppression is supported.
While the DP83847 requires an initial preamble sequence
of 32 bits for management initialization, it does not require
a full 32-bit sequence between each subsequent transac-
tion. A minimum of one idle bit between management
transactions is required as specified in IEEE 802.3u.
3.1.4 PHY Address Sensing
The DP83847 provides five PHY address pins, the informa-
tion is latched into the PHYCTRL register (address 19h,
bits [4:0]) at device power-up/Hardware reset.
The DP83847 supports PHY Address strapping values 0
(<00000>) through 31 (<11111>). Strapping PHY Address
0 puts the part into Isolate Mode. It should also be noted
that selecting PHY Address 0 via an MDIO write to PHYC-
TRL will not put the device in Isolate Mode; Address 0 must
be strapped in.
3.1.5 Nibble-wide MII Data Interface
Clause 22 of the IEEE 802.3u specification defines the
Media Independent Interface. This interface includes a
dedicated receive bus and a dedicated transmit bus. These
two data buses, along with various control and indicate sig-
nals, allow for the simultaneous exchange of data between
the DP83847 and the upper layer agent (MAC).
The receive interface consists of a nibble wide data bus
RXD[3:0], a receive error signal RX_ER, a receive data
valid flag RX_DV, and a receive clock RX_CLK for syn-
chronous transfer of the data. The receive clock can oper-
ate at either 2.5 MHz to support 10 Mb/s operation modes
or at 25 MHz to support 100 Mb/s operational modes.
The transmit interface consists of a nibble wide data bus
TXD[3:0], a transmit enable control signal TX_EN, and a
transmit clock TX_CLK which runs at either 2.5 MHz or 25
MHz.
Additionally, the MII includes the carrier sense signal CRS,
as well as a collision detect signal COL. The CRS signal
asserts to indicate the reception of data from the network
or as a function of transmit data in Half Duplex mode. The
COL signal asserts as an indication of a collision which can
occur during half-duplex operation when both a transmit
and receive operation occur simultaneously.
3.1.6 Collision Detect
For Half Duplex, a 10BASE-T or 100BASE-TX collision is
detected when the receive and transmit channels are
active simultaneously. Collisions are reported by the COL
signal on the MII.
If the DP83847 is transmitting in 10 Mb/s mode when a col-
lision is detected, the collision is not reported until seven
bits have been received while in the collision state. This
prevents a collision being reported incorrectly due to noise
on the network. The COL signal remains set for the dura-
tion of the collision.
If a collision occurs during a receive operation, it is immedi-
ately reported by the COL signal.
When heartbeat is enabled (only applicable to 10 Mb/s
operation), approximately 1µs after the transmission of
each packet, a Signal Quality Error (SQE) signal of approx-
imately 10 bit times is generated (internally) to indicate
successful transmission. SQE is reported as a pulse on the
COL signal of the MII.
3.1.7 Carrier Sense
Carrier Sense (CRS) may be asserted due to receive activ-
ity, once valid data is detected via the squelch function dur-
ing 10 Mb/s operation. During 100 Mb/s operation CRS is
asserted when a valid link (SD) and two non-contiguous
zeros are detected on the line.
For 10 or 100 Mb/s Half Duplex operation, CRS is asserted
during either packet transmission or reception.
For 10 or 100 Mb/s Full Duplex operation, CRS is asserted
only due to receive activity.
CRS is deasserted following an end of packet.
3.2 100BASE-TX TRANSMITTER
The 100BASE-TX transmitter consists of several functional
blocks which convert synchronous 4-bit nibble data, as pro-
vided by the MII, to a scrambled MLT-3 125 Mb/s serial
data stream. Because the 100BASE-TX TP-PMD is inte-
grated, the differential output pins, TD±, can be directly
routed to the magnetics.
The block diagram in Figure 5 provides an overview of
each functional block within the 100BASE-TX transmit sec-
tion.
The Transmitter section consists of the following functional
blocks:
Code-group Encoder and Injection block (bypass option)
Scrambler block (bypass option)
NRZ to NRZI encoder block
Binary to MLT-3 converter / Common Driver
Figure 3. Typical MDC/MDIO Write Operation
MDC
MDIO
00011110000000
(STA)
Idle Start
Opcode
(Write)
PHY Address
(PHYAD = 0Ch)
Register Address
(00h = BMCR)
TA
Register Data
Z
0 0 0 000 00000000
Z
Idle
1000
ZZ
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DP83847
The bypass option for the functional blocks within the
100BASE-TX transmitter provides flexibility for applications
where data conversion is not always required. The
DP83847 implements the 100BASE-TX transmit state
machine diagram as specified in the IEEE 802.3u Stan-
dard, Clause 24.
3.2.1 Code-group Encoding and Injection
The code-group encoder converts 4-bit (4B) nibble data
generated by the MAC into 5-bit (5B) code-groups for
transmission. This conversion is required to allow control
data to be combined with packet data code-groups. Refer
to Table 5: 4B5B Code-Group Encoding/Decoding for 4B to
5B code-group mapping details.
The code-group encoder substitutes the first 8-bits of the
MAC preamble with a J/K code-group pair (11000 10001)
upon transmission. The code-group encoder continues to
replace subsequent 4B preamble and data nibbles with
corresponding 5B code-groups. At the end of the transmit
packet, upon the deassertion of Transmit Enable signal
from the MAC, the code-group encoder injects the T/R
code-group pair (01101 00111) indicating the end of frame.
After the T/R code-group pair, the code-group encoder
continuously injects IDLEs into the transmit data stream
until the next transmit packet is detected (reassertion of
Transmit Enable).
3.2.2 Scrambler
The scrambler is required to control the radiated emissions
at the media connector and on the twisted pair cable (for
100BASE-TX applications). By scrambling the data, the
total energy launched onto the cable is randomly distrib-
uted over a wide frequency range. Without the scrambler,
energy levels at the PMD and on the cable could peak
beyond FCC limitations at frequencies related to repeating
5B sequences (i.e., continuous transmission of IDLEs).
The scrambler is configured as a closed loop linear feed-
back shift register (LFSR) with an 11-bit polynomial. The
output of the closed loop LFSR is X-ORd with the serial
Figure 4. 100BASE-TX Transmit Block Diagram
4B5B CODE-
GROUP ENCODER
& INJECTOR
SCRAMBLER
NRZ TO NRZI
ENCODER
5B PARALLEL
TO SERIAL
TD±
TX_CLK
TXD[3:0] /
TX_ER
100BASE-TX
LOOPBACK
MUX
BINARY TO
MLT-3 /
COMMON
DRIVER
FROM PGM
BP_4B5B
BP_SCR
MUX
DIV BY 5
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