dp83840a National Semiconductor Corporation, dp83840a Datasheet - Page 38

• Manufacturer Part Number: dp83840a
• Description: 10/100 Mb/s Ethernet Physical Layer
• Manufacturer: National Semiconductor Corporation

Version A
3.0 Functional Description
The Basic Mode Status Register (BMSR) at address 01h
indicates the set of available abilities for technology types
(bits 15 to 11, register address 01h), Auto-Negotiation
ability (bit 3, register address 01h), and Extended Register
Capability (bit 0, register address 01h). These bits are
permanently set to indicate the full functionality of the
DP83840A (only the 100BASE-T4 bit is not set since the
DP83840A does not support that function, while it does
support all the other functions).
The BMSR also provides status on:
The Auto-Negotiation Advertisement Register (ANAR) at
address 04h indicates the Auto-Negotiation abilities to be
advertised by the DP83840A. All available abilities are
transmitted by default, but any ability can be suppressed by
writing to the ANAR. Updating the ANAR to suppress an
ability is one way for a management agent to change
(force) the technology that is used.
The
(ANLPAR) at address 05h indicates the abilities of the Link
Partner as indicated by Auto-Negotiation communication.
The contents of this register are considered valid when the
Auto-Negotiation Complete bit (bit 5, register address 01h)
is set.
The Auto-Negotiation Expansion Register (ANER) at
address 06h indicates additional Auto-Negotiation status.
The ANER provides status on:
3.9.3 Auto-Negotiation Parallel Detection
The DP83840A in conjunction with the DP83223
transceiver supports the Parallel Detection function as
defined in the IEEE 802.3u specification. Parallel Detection
requires both the 10 Mb/s and 100 Mb/s receivers to
monitor the receive signal and report link status to the
Auto-Negotiation function. Auto-Negotiation uses this
information to configure the correct technology in the event
that the Link Partner does not support Auto-Negotiation yet
is transmitting link signals that the 100BASE-X or 10BASE-
T PMAs recognize as valid link signals.
The Auto-Negotiation function will only accept a valid link
signal for the purpose of Parallel Detection from PMAs
which have a corresponding bit set in the Auto-Negotiation
1. Whether Auto-Negotiation is complete (bit 5, register
2. Whether the Link Partner is advertising that a remote
3. Whether a valid link has been established (bit 2, regis-
4. Support for Management Frame Preamble suppres-
1. Whether a Multiple Link Fault has occurred (bit 4, reg-
2. Whether the Link Partner supports the Next Page func-
3. Whether the DP83840A supports the Next Page func-
4. Whether the current page being exchanged by Auto-
5. Whether the Link Partner supports Auto-Negotiation
address 01h)
fault has occurred (bit 4, register address 01h)
ter address 01h)
sion (bit 6, register address 01h)
ister address 06h)
tion (bit 3, register address 06h)
tion (bit 2, register address 06h). The DP83840A does
not support the Next Page function.
Negotiation has been received (bit1, register address
06h)
(bit 0, register address 06h)
Auto-Negotiation
Link
Partner
(Continued)
Ability
Register
38
Advertisement register, (ANAR register bits 5 and 7,
register address 04h.) This allows the DP83840A to be
configured as a 100 Mb/s only, 10 Mb/s only, or 10 Mb/s &
100 Mb/s CSMA/CD operation device depending on the
advertised abilities. The state of these bits may be modified
via the AN0 and AN1 pins (see 3.9.1 Auto-Negotiation Pin
Control) or by writing to the ANAR. For example, if bit 5 is
zero and bit 7 is one in the ANAR (i.e. 100 Mb/s CSMA/CD
only), and the Link Partner is 10BASE-T without Auto-
Negotiation, then Auto-Negotiation will not complete since
the advertised abilities and the detected abilities have no
common mode. This operation allows the DP83840A to be
used in single mode (i.e. repeater) applications as well as
dual mode applications (i.e. 10/100 nodes or switches.)
If the DP83840A completes Auto-Negotiation as a result of
Parallel Detection, bits 5 and 7 within the ANLPAR register
(register address 05h) will be set to reflect the mode of
operation present in the Link Partner. Software may
determine that negotiation completed via Parallel Detection
by reading a zero in the Link Partner Auto-Negotiation Able
bit (bit 0, register address 06h) once the Auto-Negotiation
Complete bit (bit 5, register address 01h) is set. In the
event that more than one more than one PMA indicates a
valid link, the Multiple Link Fault bit (bit 4, register address
06h) will be set.
As an example of Parallel Detection, when the Link Partner
supports 100BASE-TX but does not support Auto-
Negotiation, Parallel Detection will allow the DP83840A to
negotiate to 100 Mb/s Half Duplex operation by detecting a
valid set of IDLEs even though no Link Code Words were
exchanged through FLP Bursts. A similar process on
connection to a Link Partner that supports 10BASE-T but
does not support Auto-Negotiation (i.e. the majority of
installed 10BASE-T connections), where the DP83840A
will negotiate to 10BASE-T Half Duplex operation by
detecting valid link pulses separated by 8-24 ms.
3.9.4 Auto-Negotiation Restart
Once Auto-Negotiation has completed it may be restarted
at any time by setting bit 9 of the BMCR to one. If the mode
configured by a successful Auto-Negotiation loses a valid
link, then the Auto-Negotiation process will resume and
attempt to determine the configuration for the link. This
function ensures that a valid configuration is maintained if
the cable becomes disconnected.
A renegotiation request from any entity, such as a
management agent, will cause the DP83840A halt any
transmit
break_link_timer expires (1500ms). Consequently, the Link
Partner will go into link fail and normal Auto-Negotiation
resumes. TheDP83840A will resume Auto-Negotiation
after the break_link_timer has expired by issuing FLP (fast
Link Pulse) bursts.
3.9.5 Enabling Auto-Negotiation via Software
It is important to note that if the DP83840A has been
initialized upon power-up as a non-auto-negotiating device
(forced technology), and it is then required that auto-
negotiation of re-auto-negotiation be initiated via software,
bit 12 of the Basic Mode Control Register (address 00h)
must first be cleared and then set for any auto-negotiation
function to take effect.
data
National Semiconductor
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link
pulse
activity
until
the