ENC28J60-CSLASHSP datasheet(33/96 Pages) MICROCHIP

33 / 96 page

Preliminary

DS39662B-page 31

ENC28J60

5.0

ETHERNET OVERVIEW

Before discussing the use of the ENC28J60 as an

Ethernet interface, it may be helpful to review the

structure of a typical data frame. Users requiring more

information should refer to IEEE Standard 802.3 which

is the basis for the Ethernet protocol.

5.1

Packet Format

Normal IEEE 802.3 compliant Ethernet frames are

between 64 and 1518 bytes long. They are made up of

five or six different fields: a destination MAC address, a

source MAC address, a type/length field, data payload,

an optional padding field and a Cyclic Redundancy

Check (CRC). Additionally, when transmitted on the

Ethernet medium, a 7-byte preamble field and start-of-

frame delimiter byte are appended to the beginning of

the Ethernet packet. Thus, traffic seen on the twisted

pair cabling will appear as shown in Figure 5-1.

5.1.1

PREAMBLE/START-OF-FRAME

DELIMITER

When transmitting and receiving data with the

ENC28J60, the preamble and start of frame delimiter

bytes will automatically be generated or stripped from

the packets when they are transmitted or received. The

host controller does not need to concern itself with

them. Normally, the host controller will also not need to

concern itself with padding and the CRC which the

ENC28J60 will also be able to automatically generate

when transmitting and verify when receiving. The

padding and CRC fields will, however, be written into

the receive buffer when packets arrive, so they may be

evaluated by the host controller if needed.

FIGURE 5-1:

ETHERNET PACKET FORMAT

Padding

FCS(1)

Number

Field

Comments

46-1500

Destination Address,

such as Multicast, Broadcast or Unicast

Source Address

Packet Payload

Frame Check Sequence – CRC

Type/Length

Data

of Bytes

Type of Packet or the Length of the Packet

(with optional padding)

Preamble

Filtered out by the Module

SFD

Start-of-Frame Delimiter

(filtered out by the module)

Used in the

Calculation

of the FCS

Note 1:

The FCS is transmitted starting with bit 31 and ending with bit 0.

ENC28J60-C/SP 数据表(PDF) 33 Page - Microchip Technology

ENC28J60-C/SP 数据表(HTML) 33 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96

数据表下载