STE100A datasheet(20/82 Pages) STMICROELECTRONICS

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Functional description

STE10/100A

20/82

3.5

Network operation

3.5.1

MAC operation

The MAC (Media access control) portion of STE10/100A incorporates the essential protocol

requirements for operating as an IEEE802.3 and ethernet compliant node.

Format

Transmit data encapsulation

The differences between transmit data encapsulation and a MAC frame while operating in

100BASE-TX mode are listed as follows:

–

The first byte of the preamble is replaced by the JK code according to IEE802.3u,

clause 24.

–

After the CRC field of the MAC frame, the STE10/100A will insert the TR code

according to IEE802.3u, clause 24.

Receive data decapsulation

When operating in 100BASE-TX mode the STE10/100A detects a JK code in a preamble as

well as a TR code at the packet end. If a JK code is not detected, the STE10/100A will abort

the reception of the frame and wait for a new JK code detection. If a TR code is not

detected, the STE10/100A will report a CRC error.

Deferring

The inter-frame gap (IFG) time is divided into two parts:

–

FG1 time (64-bit time): If a carrier is detected on the medium during this time, the

STE10/100A will reset the IFG1 time counter and restart to monitor the channel for

an idle again.

–

IFG2 time (32-bit time): After counting the IFG2 time the STE10/100A will access

the channel even though a carrier has been sensed on the network.

Table 2.

Format

Field

Description

Preamble

A 7-byte field of (10101010b)

Start frame diameter

A 1-byte field of (10101011b)

Destination address

A 6-byte field

Source address

A 6-byte field

Length/type

A 2-byte field indicated the frame is in IEEE802.3 format or

ethernet format.

IEEE802.3 format: 0000H ~ 05DCH for length field

Ethernet format: 05DD ~ FFFFH for type field

Data

46(1) ~ 1500 bytes of data information

If padding is disabled (TDES1 bit 23), the data field may be shorter than 46 bytes

CRC

A 32-bit cyclic redundancy code for error detection

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