MB86960 Datasheet, PDF (32/65 Pages) Fujitsu Component Limited. – NETWORK INTERFACE CONTROLLER with ENCODER/DECODER (NICE)

MB86960
NODE ID REGISTERS
The Node ID Registers are accessed in register bank “0” at
register addresses xxx8H–xxxDH. During initialization
of the node, the unique Ethernet address assigned to the
node is loaded into these registers. The first register at
xxx8H corresponds to the first byte of the Node ID, which
corresponds to the first address byte to be received as a
packet arrives from the network. If the chip is configured
to do so in its Address Filter mode bits, DLCR5<1:0>, the
destination address field of an incoming packet will be
compared to the Node ID stored in these registers. If there
is a match, provided the packet passes the error filter, it
will be accepted.
These registers are readable as well as writable, but they
should not be accessed while the receiver is enabled. To
avoid interaction with the receiver, access these registers
only when DLC EN is 1. It is recommended that they be
written and read only during initialization before
enabling the receiver, i.e. before writing 0 to DLC EN,
DLCR6<7>.
The address contained in these registers is used only for
receive (destination) address filtering, not for the source
address of outgoing packets. Outgoing packet addresses
must be provided by the system as part of the packet data.
Within each byte, the bits are transmitted and received on
the network least-significant bit first. See Table 3 for the
transmission bit order, which follows the bit numbering
in this table.
Time Domain Reflectometry (TDR) Counter
The TDR Counter can be used to get a rough indication of
the location of a fault on the network, if one exists. When
a node transmits, a short or open on the network would
cause a reflected signal to the node’s receiver which can
sometimes be detected. The reflection will cause the
carrier sense to fail and/or a false collision to be detected.
This affect, time domain reflectometry, can be used to
estimate the distance along the network cable from the
node to the fault. The TDR Counter counts the number of
bits transmitted before either a collision occurs, or carrier
sense is lost, whichever comes first. If neither occur
during transmission of the packet, the count is cleared.
The amount of elapsed time this represents is two (2)
times the signal delay from the node to the fault. An open
on the network will usually cause a false collision,
whereas a short is more likely to cause loss of carrier
sense.
The TDR Count comes from DLCR14 and 15. DLCR14
is the least-significant byte, DLCR15 the most-signifi-
cant. Only the lower 14 bits of the counter are equipped,
which is more than is needed for an IEEE or Ethernet
LAN. (The top two bits, DLCR15<7:6>, are always 0.)
To perform the TDR test for a fault, first enable interrupts
for transmitter done (TX DONE). This is done by setting
DLCR2<7> high. (An alternative to using the interrupt
would be polling the TX DONE bit looking for a high
level.) Set the 16 Collisions Register, BMPR11, to 07H
for this test (no halt, skip failed packet). Clear all status
bits by writing FF86H to the Receive and Transmit Status
Registers. Next, transmit, or attempt to transmit, a packet
of 600 bits or more in length. Up to 16 attempts may be
made automatically if collisions are being indicated.
Upon completion of the transmission attempt(s) TX
DONE will go high, generating an interrupt if enabled.
When this occurs, read the Transmit Status Register and
the TDR Register.
Interpreting the results: If the count is zero, no fault was
detected. If the count is greater than zero but smaller than
the packet length, it may indicate a cable fault. If the count
is less than 525, there may have been a real collision
occurring during the test. Real collisions normally occur
within the first 65 bytes of the packet, including
preamble. Take note of the error messages, COL and CR
LOST. COL high suggests a cable open, whereas CR
LOST suggests a short. It is best to repeat the
measurement several times, then throw out the
anomalous values, if any, and average the rest. A cluster
of readings at about the same value is a strong indicator
of a valid fault measurement. If such a cluster of readings
occurs, multiply the average of the cluster by 39 feet to
estimate the distance from the node to the fault. (39 ft. =
(100 ns x .8 x 186,282 mi/s x 5280 ft/mi)/2 ... this
assumes the network is mostly coaxial cable with signal
propagation speed of approximately .8 x C, the speed of
light.)