STE10 Datasheet, PDF (49/66 Pages) STMicroelectronics – PCI 10/100 ETHERNET CONTROLLER WITH INTEGRATED PHY 5V

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.
s Format
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
*Note: If padding is disabled (TDES1 bit 23), the data field may be shorter than 46 bytes.
s 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.
s 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.
s 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.
s 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^k where k = min(n, 10)
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