MB86967 Datasheet, PDF (34/129 Pages) Fujitsu Component Limited. – LAN Controller with PC Card, ISA Bus, and General-purpose Bus Interfaces

MB86967
10.8 Collision Detection
The collision detection function operates on the twisted-pair side of the interface. A collision is defined as the
simultaneous presence of valid signals on both the TPI circuit and the TPO circuit. The transceiver reports
collisions to the back-end via an internal signal. If the TPI circuit is active while there is activity on the TPO
circuit, the TPI data passes to the back-end as received data, disabling normal loopback.
10.9 Loopback
The MB86967 provides the automatic local loopback function specified by the 10BASE-T standard for the twisted-
pair port. This function is in effect except when the LBC bit, DLCR4<1>, is asserted. Data transmitted by the
transmitter is passed through the data encoder, internally looped back within the MB86967 before the TPO
drivers to the data decoder and returned to the receiver. This local loopback function is disabled when a data
collision occurs, clearing the received data circuit in the transceiver for the data arriving at the twisted-pair inputs.
The local loopback is also disabled during the link fail and jabber states.
The MB86967 provides additional loopback testing functions controlled by LBC. When the twisted-pair port is
selected and LBC is asserted, the loopback is forced regardless of the state of the TPI inputs or link test failure.
During loopback, data is routed from the transmit buffer to the transmit section of the data link controller, through
the Manchester encoder, back through the Manchester decoder, through the receiver section of the data link
controller, and is then stored in the receive buffer. Software can then read and check the received packet that
has traveled through the MB86967 transmit and receive sections. Receipt of the loopback data into the receive
buffer can be disabled by asserting FILTER SELF RX, BMPR14<0>. The transmitted data is blocked from
appearing at the network outputs while the MB86967 is in forced loopback mode (LBC asserted).
10.10 Link Integrity Test
The link integrity test determines the status of the receive side twisted-pair cable. Link integrity testing is enabled
when LINK TEST EN, BMPR13<5>, is set low. When enabled, the receiver recognizes the link integrity pulses
transmitted in the absence of receive traffic. If no serial data stream or link integrity pulses are detected within
50 to 150 milliseconds, the MB86967 enters a link-fail state and disables the transmit and automatic local
loopback functions. The MB86967 ignores any link integrity pulse with an interval less than 2 to 7 milliseconds.
The MB86967 remains in the link-fail state until it detects either a serial data packet or two or more link integrity
pulses.
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