7.0 Hardware User Information (Continued)
Basic Mode Status Register (01h). The Link Status bit must are not, such as the DP83840, which will transmit data
be read twice, since it’s a latched bit. If bit 2 and bit 5 are before Good Link Status is achieved. The problem with the
set to
a logic 1, then Auto-Negotiation completed 10 Mb/s is very limited. It only happen when Auto-
successfully. Bits 6 and 7 in the Phy Address Register Negotiation is initiated by software (i.e. writing 1200h to
(19h) contain the information on Speed and Duplex (FD/ BMCR), and does not happen with un-plugging and re-
HD).
plugging of cable, or H/W or S/W reset. Since there are
very few 10 Mb/s only DP83840 Legacy devices out in the
market, the possibilities of not able to Auto-Negotiate with
10 Mb/s device is very minimal.
If the Link_Status bit OR the Auto-Negotiation Complete bit
are still logic 0 (bits 2 and 5) in the Basic Mode Status
Register (01h), then negotiation did not complete. Read bit
4 (Multiple Link Fault) in the Auto-Negotiation Expansion Symptoms:
Register (06h). ANER bit 4 must be read twice, since it’s a
When the DP83840A receives packet data during Auto-
latched bit. If the Multiple Link Fault bit is set to a logic 1,
then the device can be forced into 100 Mb/s Half-Duplex
operation via register control.
Negotiation, the Auto-Negotiation state machine thinks that
there are multiple links present and sets the Multiple Link
Fault Bit (bit 4) in the AUTO-NEGOTIATION EXPANSION
On the Basic Mode Control Register (00h) set bit 12 (Auto- REGISTER (06h). The problem can be seen with 64 byte
Negotiation Enable) to a logic 0, set bit 13 (Speed 100 Mb/s packets with Inter-Packet-Gaps (IPG) of less
Selection) to a logic 1 for 100 Mb/s operation, and bit 8 to than 5us, or 64-128 byte 10 Mb/s packets with IPG of
logic 0 for Half-Duplex operation. (i.e. write 2000h to the 9.6us.
Basic Mode Control Register). This disables Auto-
Negotiation and puts the part into 100 Mb/s mode.
Solution/Workaround:
The same workaround described in 011.E (Auto-
Check Link Status (bit 2 of Basic Mode Status Register) bit
Negotiating to Link Partner Sending 100 Mb/s Scrambled
by reading BMSR register twice. If bit 2 is set to “1”, then
Idles) will also work with this problem:
the local node/port is linked to the non Auto-Negotiation
A.) Manually configure the system using the DP83840A
into 100 Mb/s or 10 Mb/s mode through software. Many
installation programs already support this capability.
100 Mb/s partner.
If bit 2 of the BMSR is not set, then force the device into 10
Mb/s mode by writing 0000h to BMCR register (00h).
B.) Modify software driver to detect fault condition.
7.4 HBE Disable in 10 Mb/s Repeater Mode
Problem:
Check Link Status (bit 2 of Basic Mode Status Register) bit
by reading BMSR register twice. If bit 2 is set to “1”, then
the local node/port is linked to the non Auto-Negotiation 10
Mb/s partner.
According to the 802.3 IEEE specification Heart Beat
Enable (HBE) must be disabled when used in
repeaters.The DP83840A when put into 10 Mb/s repeater
mode does not disable HBE automatically and must be set
manually.
National is evaluating a silicon fix to correct this problem.
Please contact your Sales Representative for the current
status.
Description:
7.3 840A Auto-Negotiating to Legacy Devices
Problem:
Approximately 1.6µs after the end of a packet the COL line
will become active for approximately 1.3µs. A repeater
using the COL line to determine collisions or gather
collision statistics will misinterpret the HBE signal as a valid
collision.
The DP83840A will not always complete Auto-Negotiation
when Auto-Negotiating with a 100 Mb/s or 10 Mb/s link
partner that is sending out packet data before link has been
establish.
Symptoms:
Description:
With HBE enabled in repeater mode the COL line will
become active after the end of packet and cause the
repeater to falsely detect collision activity.
The DP83840A in Auto-Negotiation mode is not always
able to establish link with a 100 Mb/s link partner that is
sending out scrambled packet data. The reason for this is
that the DP83840A is expecting to see only 100 Mb/s idles,
Fast Link Pulses (FLPs), or Normal Link Pulses (NLPs) and
not scrambled packet data. When the DP83840A sees
scrambled packet data, it can be misconstrued as NLPs
and FLPs, which confuses the Auto-Negotiation state
machine.
Solution/Workaround:
HBE can be disabled by writing a 0 to bit 4 (HBE) in the
10BASE-T CONFIGURATION REGISTER (1Ch).
HBE can also be disabled by putting the part is in Full-
Duplex mode.
The DP83840A in Auto-negotiation mode may not able to
complete Auto-Negotiation with a 10 Mb/s link partner that
is sending out packets prior to getting a good link. The
reason for this is that the DP83840A can mis-identify some
specific 10 Mb/s packet energy as 100 Mb/s data. When
the DP83840A receives those specific 10 Mb/s packet, it
will get confused on which speed to detect.
7.5 CRS Glitching in10 Mb/s Repeater Mode
Problem:
When the DP83840A is put into 10 Mb/s repeater mode
and receives a non-101010... jam pattern, Carrier Sense
(CRS) will glitch during collision. This will cause problems
when used in repeater applications where CRS is used to
determine collisions. The collision signals from the
DP83840A behave normally.
The 802.3U IEEE specification does not allow transmission
of data prior to getting Good Link Status. The DP83840A is
compliant to this specification, but some Legacy devices
Version A
National Semiconductor
68
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