Owner's manual

Table Of Contents
9-4 DS785UM1
Copyright 2007 Cirrus Logic
1/10/100 Mbps Ethernet LAN Controller
EP93xx User’s Guide
9
9
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Figure 9-2. Ethernet Frame / Packet Format (Type II only)
In the receiver, the MAC detects the preamble and locks onto the embedded clock. The MAC
performs destination address filtering (individual, group, broadcast, promiscuous) on the DA.
The MAC engine computes the correct FCS, and reports if the received FCS is “good” or
“bad”. The data after the SFD and before the FCS is supplied to the host as the received
data. The received FCS may also be passed to the host by setting RXCtl.BCRC.
Ethernet Frame/Packet Format (Type II, only)
1 byteup to 7 bytes 6 bytes 6 bytes
optional field
2 bytes
LLC data Pad FCS
N bytes M bytes 4 bytes
preamble
frame length
min 64 bytes
max 1518 bytes
alternating 1s / 0s SFD D A SA
SFD = Start of Frame Delimiter
DA = Destination Address
SA = Source Address
LLC = Logical Link Control
FCS = Frame Check Sequence (sometimes
called Cyclic Redundancy Check, or CRC)
The optional field, which is two bytes
long, is either a TYPE field for Ethernet
applications,or is a LENGTH field for
IEEE 802.3 applications.
D
irection of Transmission
The Pad field will be used only to get
the frame to the minimum size.
See paragraph 6.3.3.
When the CS8931 adds pad bytes,
the pad is the last byte of the
LLC data field repeated M times.
Frame
Packet