STE100A データシートの表示（PDF） - STMicroelectronics
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STE100A Datasheet PDF : 82 Pages
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Functional description
STE10/100A
3.5
3.5.1
Network operation
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
Table 2. Format
Field
Description
Preamble
Start frame diameter
A 7-byte field of (10101010b)
A 1-byte field of (10101011b)
Destination address
Source address
Length/type
Data
CRC
A 6-byte field
A 6-byte field
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
46(1) ~ 1500 bytes of data information
A 32-bit cyclic redundancy code for error detection
1. 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:
– 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.
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