Motorola MPC8260 - Manual (Page 876)

30-2 MPC8260 PowerQUICC II UserÕs Manual MOTOROLA
Part IV. Communications Processor Module
on the LAN. If a collision is detected, the station forces a jam signal (all ones) on its frame
and stops transmitting. Collisions usually occur close to the beginning of a frame. The
station then waits a random time period (backoff) before attempting to send again. When
the backoff completes, the station waits for silence on the LAN and then begins
retransmission on the LAN. This process is called a retry. If the frame is not successfully
sent within 15 retries, an error is indicated.
10-Mbps Ethernet basic timing speciÞcations follow:
¥ Transmits at 0.8 µs per byte
¥ The preamble plus start frame delimiter is sent in 6.4 µs.
¥ The minimum interframe gap is 9.6 µs.
¥ The slot time is 51.2 µs.
100-Mbps Ethernet basic timing speciÞcations follow:
¥ Transmits at 0.08 µs per byte
¥ The preamble plus start frame delimiter is sent in 0.64 µs.
¥ The minimum interframe gap is 0.96 µs.
¥ The slot time is 5.12 µs.
30.1 Fast Ethernet on the MPC8260
When a general FCC mode register (GFMRx[MODE]) selects Ethernet protocol, that FCC
performs the full set of IEEE 802.3/Ethernet CSMA/CD media access control (MAC) and
channel interface functions. Figure 30-2 shows a block diagram of the FCC Ethernet
control logic.