DP83850CVF National Semiconductor, DP83850CVF Datasheet - Page 10

• Manufacturer Part Number: DP83850CVF
• Description: IC CONTROLLER INTERFACE 132-PQFP
• Manufacturer: National Semiconductor

Specifications of DP83850CVF

• Controller Type: Ethernet Repeater Interface Controller
• Interface: Serial
• Voltage - Supply: 4.75 V ~ 5.25 V
• Current - Supply: 295mA
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 132-MQFP, 132-PQFP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: *DP83850CVF

3.0 Functional Description
The following sections describe the different functional
blocks of the DP83850C 100 Mb/s Repeater Interface Con-
troller. The IEEE 802.3u repeater specification details a
number of functions a repeater system is required to per-
form. These functions are split between those tasks that
are common to all data channels and those that are spe-
cific to each individual channel. The DP83850C follows
this split task approach for implementing the required func-
tions. Where necessary, the difference between the TX and
T4 modes is discussed.
3.1 Repeater State Machine
The Repeater State Machine (RSM) is the main block that
governs the overall operation of the repeater. At any one
time, the RSM is in one of the following states: Idle,
Repeat, Collision, One Port Left, or Noise.
3.1.1 Idle State
The RSM enters this state after reset or when there is no
activity on the network and the carrier sense is not present.
The RSM exits from this state if the above conditions are
no longer true.
3.1.2 Repeat State
This state is entered when there is a reception on only one
of the ports, port N. While in this state, the data is transmit-
ted to all the ports except the receiving port (port N). The
RSM either returns to Idle state when the reception ends,
or transitions to Collision state if there is reception activity
on more than one port.
3.1.3 Collision State
When there is receive activity on more than one port of the
repeater, the RSM moves to Collision state. In this state,
transmit data is replaced by Jam and sent out to all ports
including the original port N.
There are two ways for the repeater to leave the Collision
state. The first is when there is no receive activity on any
of the ports. In this case, the repeater moves to Idle state.
The second is when there is only one port experiencing
collision in which case the repeater enters the One Port
Left state.
3.1.4 One Port Left State
This state is entered only from the Collision state. It guar-
antees that repeaters connected hierarchically will not jam
each other indefinitely. While in this state, Jam is sent out
to all ports except the port that has the receive activity. If
more receive activity occurs on any other port, then the
repeater moves to Collision state.
Otherwise, the repeater will transition to Idle state when the
receive activity ends.
3.1.5 Noise State
When there is an Elasticity Buffer overflow or underflow
during packet reception, then the repeater enters the Noise
state. During this state, the Jam pattern is sent to all trans-
mitting ports. The repeater leaves this state by moving
either to the Idle state, if there is no receive activity on any
ports, or to the Collision state, if there is a collision on one
of its segments.
3.2 RXE Control
When only one port has receive activity, the RXE signal
(receive enable) is activated. If multiple ports are active
(i.e. a collision scenario), then RXE will not be enabled for
10
any port. The Port Select Logic asserts the open-collector
outputs /IR_COL_OUT and /IR_ACTIVE to indicate to
other cascaded DP83850Cs that there is collision or
receive activity present on this DP83850C.
The polarity of the RXE signal can be set through an exter-
nal pull down resistor placed at the RSM[3] pin. That is, if
the RSM[3] pin is unconnected or pulled high, then the
RXE is active high and when the RSM[3] is pulled low, then
the RXE is active low.
3.3 TXE Control
This control logic enables the appropriate ports for data
transmission according to the four states of the RSM. For
example, during Idle state, no ports are enabled; during
Repeat state, all ports but port N are enabled; in Collision
state, all ports including port N are enabled ; during One
Port Left state, all ports except the port experiencing the
collision will be enabled.
3.4 Data Path
After the Port Selection logic has enabled the active port,
receive data (RXD), receive clock (RXC), receive error
(RX_ER) and receive data valid (RX_DV) will flow through
the chip from that port out onto the Inter Repeater (IR) bus
if no collisions are present. The signals on the IR bus flow
either in to or out of the chip depending upon the
Repeater’s state.
If the DP83850C is currently receiving and no collisions are
present, the IR signals flow out of the chip. The
DP83850C's Arbitration Logic guarantees that only one
DP83850C will gain ownership of the IR bus. In all other
states, the IR signals are inputs.
When IR signals are inputs, the signals flow into the Elas-
ticity Buffer (EB). Here, the data is re-timed and then sent
out to the transmit ports. The Transmit Control logic deter-
mines which ports are enabled for data transmission.
If a collision occurs, a Jam pattern is sent out from the EB
instead of the data. The Jam pattern (3,4,3,4,..... from the
DP83850C, encoded by the Physical Layer device as
1,0,1,0,.....) is transmitted for the duration of the collision
activity.
If the repeater is configured in the preamble regeneration
mode (T4 mode), approximately 12 clock cycles after the
assertion of /IR_ACTIVE (indicating a packet reception on
a segment), the 100RIC begins to transmit the preamble
pattern onto the other network segments. While the pre-
amble is being transmitted, the EB monitors the received
clock and data signals. When the start of the frame delim-
iter "SFD" is detected, the received data stream is written
into the EB. After this point, data from the EB is sent out to
the Transmit interface. The preamble is always generated
in its entirety (i.e. fifteen 5’s and one D) even if a collision
occurs.
3.5 Elasticity Buffer
The elasticity buffer, or a logical FIFO buffer, is used to
compensate for the variations and timing differences
between the recovered Receive Clock and the local clock.
This buffer supports maximum clock skews of 200ppm for
the preamble regeneration (T4) mode, and 100ppm for the
TX mode, within a maximum packet size of 1518 bytes.
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