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STE10/100

6.5 Network Operation

6.5.1 MAC Operation

The MAC (Media Access Control) portion of STE10/100 incorporates the essential protocol requirements for op-

erating as an IEEE802.3 and Ethernet compliant node.

Format

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

Transmit Data Encapsulation

The differences between transmit data encapsulation and a MAC frame while operating in 100BASE-

TX mode are listed as follows:

1. The first byte of the preamble is replaced by the JK code according to IEE802.3u, clause 24.

2. After the CRC field of the MAC frame, the STE10/100 will insert the TR code according to IEE802.3u,

clause 24.

Receive Data Decapsulation

When operating in 100BASE-TX mode the STE10/100 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 STE10/100 will abort the reception of the frame

and wait for a new JK code detection. If a TR code is not detected, the STE10/100 will report a CRC

error.

Deferring

The Inter-Frame Gap (IFG) time is divided into two parts:

1.IFG1 time (64-bit time): If a carrier is detected on the medium during this time, the STE10/100 will

reset the IFG1 time counter and restart to monitor the channel for an idle again.

2.IFG2 time (32-bit time): After counting the IFG2 time the STE10/100 will access the channel even

though a carrier has been sensed on the network.

Collision Handling

The scheduling of re-transmissions are determined by a controlled randomization process called

“truncated binary exponential back-off”. At the end of enforcing a collision (jamming), the STE10/100

delays before attempting to re-transmit the packet. The delay is an integer multiple of slot time. The

number of slot times to delay before the nth re-transmission attempt is chosen as a uniformly distributed

integer r in the range:

0 · r < 2

where k = min(n, 10)

Field

Description

Preamble

A 7-byte field of (10101010b)

Start Frame Delimiter

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 ~ 1500 bytes of data information

CRC

A 32-bit cyclic redundancy code for error detection

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