DP83840AVCE National Semiconductor, DP83840AVCE Datasheet - Page 40

• Manufacturer Part Number: DP83840AVCE
• Description: IC ETHERNET PHYS LAYER 100-PQFP
• Manufacturer: National Semiconductor

Specifications of DP83840AVCE

• Controller Type: Ethernet Controller, 10Base-T
• Interface: IEEE 802.3af
• Voltage - Supply: 4.75 V ~ 5.25 V
• Current - Supply: 335mA
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 100-MQFP, 100-PQFP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: *DP83840AVCE

Version A
3.0 Functional Description
3.11 LOOPBACK OPERATION
The DP83840A supports several different modes of
loopback operation for diagnostic purposes.
3.11.1 10BASE-T Loopback
The loopback option for 10BASE-T operation can be
selected via the serial MII either by asserting the Loopback
bit (bit 14) in the Basic Mode Control Register (address
00h), or by asserting the 10BT_LPBK bit (bit 11) in the
Loopback, Bypass and Receiver Error Mask Register
(address 18h). Asserting either of these bits will cause the
10BASE-T data present at the transmit MII data inputs to
be routed through the entire 10BASE-T transceiver and
back to the receive MII data outputs. During this loopback
mode, the Manchester encoded 10BASE-T data will not be
present at either the TXU+/- or TXS+/- serial differential
outputs.
Normal 10BASE-T operation, in order to be standard
compliant, also loops back the MII transmit data to the MII
receive data. However, the data is also allowed to pass
through the 10BASE-T transmitter and out either the
TXU+/- or TXS+/- outputs as well.
3.11.2 100BASE-X Loopback
The loopback options for 100BASE-X operation can be
selected by asserting the Loopback bit (bit 14) in the Basic
Mode Control Register (address 00h), or by selecting the
desired mode as determined by the LB[1:0] (bits 9 and 8) in
the Loopback, Bypass and Receiver Error Mask Register
(address 18h).
Asserting the Loopback bit (bit 14) in the Basic Mode
Control Register (address 00h) will cause the same
loopback of MII transmit to MII receive as described
previously in the 10BASE-T loopback section, except at 25
MHz due to 100BASE-X operation.
The LB[1:0] bits (bits 9 and 8) of the LBREMR (address
18h) allow for three different modes of operation:
The first mode allows normal operation without any form of
loopback.
The second mode asserts the LBEN output of the
DP83840A which, when connected to the LBEN input of
the twisted pair transceiver (DP83223A), forces the twisted
pair transceiver into loopback mode. Therefore, when the
DP83840A is transmitting 100BASE-X serial data from its
serial TD+/- outputs to the twisted pair transceiver, this
data is immediately routed back to the RD+/- 100BASE-X
serial inputs of the DP83840A device.
The third mode selects the Remote Loopback operation. In
this mode, the DP83840A device serves as a “remote
loopback” for the far end partner. Serial data received off
the twisted pair cable is routed, via the DP83223A, into the
RD+/- serial inputs of the DP83840A where it is then routed
back to the TD+/- serial outputs of the DP83840A and
finally launched back onto the twisted pair cable, via the
DP83223A, and sent back to the far-end partner.
In each of the 100BASE-X loopback modes, except for
Remote Loopback, the assertion of the loopback function
1. bit 9 = 0, bit 8 = 0; Normal operation without loopback
2. bit 9 = 0, bit 8 = 1; PMD loopback operation
3. bit 9 = 1, bit 8 = 0; Remote Loopback
(Continued)
40
will result in a 550 s down-time where the 100BASE-TX
descrambler must reacquire synchronization with the
scrambled data stream before any valid data will appear at
the receive MII RXD[3:0] outputs.
3.12 ALTERNATIVE 100BASE-X OPERATION
The DP83840A 10/100 Physical Layer device supports one
standard and three alternative modes when operating at
100 Mb/s.
3.12.1 Translational (normal) Mode
The first mode is referred to as the “Translational” mode.
This is the standard and most commonly used operating
mode where all transmit and receive functions are enabled
in order to condition the data as it flows through the
Physical Layer between the MAC and cable. All of the
transmit and receive blocks as depicted in Figures 4 and 5
are enabled (not bypassed).
3.12.2 Transparent Mode
The second mode is referred to as “Transparent”. In this
mode, the 4B/5B translators in both the transmit and
receive sections are bypassed as might be required in
certain repeater applications. This is accomplished either
by configuring the BP4B5B pin (100) of the DP83840A to a
logic high level prior to power-up/hardware reset or by
setting the BP_4B5B bit (bit 14) of the LBREMR register
(address 18h).
In “Transparent” mode, all remaining functional blocks
within the 100BASE-X transmit and receive sections are
still operational. This allows the 5B serial code-group on
the twisted pair to be presented as descrambled data,
without conversion to 4B, to the MII. Since the MII normally
only carries a nibble wide word, the fifth bit, which is the
new MSB, is carried on the RX_ER and TX_ER signals for
receive and transmit operations respectively.
In the “Transparent” mode, all of the clock to data timing for
both MII transmit and MII receive operations remains the
same as in “Translational” mode. However, upon reception
of a packet, the /J/K/ start of stream delimiter is not
replaced by the /5/5/ MAC preamble nor is the /T/R/ end of
stream delimiter removed from the packet before
presentation to the MII receive RXD[3:0] and RX_ER
outputs. Similarly, the transmit MII data TXD[3:0] and
TX_ER must already have /J/K/ and /T/R/ packet delimiters
in place. Therefore, the repeater controller device is
responsible for receiving the packet delimiters intact as well
as transmitting these delimiters intact back to the
DP83840A device(s).
The receive data valid flag, RX_DV, operates the same
during “Transparent” mode as it does in “Translational”
mode. Additionally, Idles are passed to and from the MII as
/00000/.
Finally, the “Transparent” mode of operation will operate
the same when the DP83840A is in either node mode or
repeater mode with the only difference being CRS
functionality. As in “translational” mode, if the DP83840A is
configured for repeater operation, the CRS signal will be
suppressed during transmit such that only actual network
collisions will be flagged.
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