K60P100M100SF2RM Datasheet, PDF (1194/1809 Pages) Freescale Semiconductor, Inc – K60 Sub-Family Reference Manual

Functional Description
44.4.5.5 Collision Detection and Handling — Half Duplex Operation
Only
A collision occurs on a half-duplex network when concurrent transmissions from two or
more nodes take place. During transmission, the core monitors the line condition and
detects a collision when the PHY device asserts MII_COL.
When the core detects a collision while transmitting, it stops transmission of the data and
transmits a 32-bit jam pattern. If the collision is detected during the preamble or the SFD
transmission, the jam pattern is transmitted after completing the SFD, which results in a
minimum 96-bit fragment. The jam pattern is a fixed pattern that is not compared to the
actual frame CRC and has a very low probability (0.532) of having a jam pattern identical
to the CRC.
If a collision occurs before transmission of 64 bytes (including preamble and SFD), the
MAC core waits for the back-off period and retransmits the packet data (stored in a 64-
byte re-transmit buffer) already sent on the line. The backoff period is generated from a
pseudo-random process (truncated binary exponential backoff).
If a collision occurs after transmission of 64 bytes (including preamble and SFD), the
MAC discards the remainder of the frame, optionally sets the LC interrupt bit, and sets
TxBD[LCE].
MAC Tx Engine
MAC FIFO
Retransmit
Buffer
Control
64x8
Retransmit
Buffer
Enable
Frame
Discard
Backoff
Period
MAC Transmit
Control
MAC Transmit
Datapath
Figure 44-57. Packet Re-Transmit Overview
1194
K60 Sub-Family Reference Manual, Rev. 6, Nov 2011
Freescale Semiconductor, Inc.