Freescale Semiconductor PowerQUICC MPC885 Reference Manual page 757

Powerquicc family

Table of Contents

SCC Ethernet Mode

This chapter describes SCC ethernet functionality as specifically implemented on the MPC885. To ensure

proper implementation of other derivatives of the MPC885 family,

reference of the fundamental differences. The appropriate appendix should be consulted for further

information.

SCC Ethernet

The ethernet IEEE 802.3 protocol is a widely used LAN protocol based on the carrier sense multiple

access/collision detect (CSMA/CD) approach. Because ethernet and IEEE 802.3 protocols are similar and

can coexist on the same LAN, both are referred to as ethernet in this manual, unless otherwise noted.

shows ethernet and IEEE 802.3 frame structure.

Note: The lsb of each octet is transmitted first.

The frame begins with a 7-byte preamble of alternating ones and zeros. Because the frame is Manchester

encoded, the preamble gives receiving stations a known pattern on which to lock. The start frame delimiter

follows the preamble, signifying the beginning of the frame. The 48-bit destination address is next,

followed by the 48-bit source address. Original versions of the IEEE 802.3 specification allowed 16-bit

addressing, but this addressing has never been widely used and is not supported.

The next field is the ethernet type field/IEEE 802.3 length field. The type field signifies the protocol used

in the rest of the frame and the length field specifies the length of the data portion of the frame. For ethernet

and IEEE 802.3 frames to coexist on the same LAN, the length field of the frame must always be different

from any type fields used in ethernet. This limits the length of the data portion of the frame to 1,500 bytes

Freescale Semiconductor

Table 27-1. MPC885 Family

Figure 27-1. Ethernet Frame Structure

MPC885 PowerQUICC Family Reference Manual, Rev. 2

is provided as a quick

Documentation

Frame Length is

64–1518 Bytes

46–1500 Bytes