ETHERNET CONTROLLER
S3C2500B
7-4
7.3.2 PHYSICAL LAYER ENTITY (PHY)
The physical layer entity, or PHY, performs all of the decoding/encoding on incoming and outgoing data. The
manner of decoding and encoding (Manchester for 10BASE-T, 4B/5B for 100BASE-X, or 8B/6T for 100BASE-T4)
does not affect the MII. The MII provides the raw data it receives, starting with the preamble and ending with the
CRC. The MII expects raw data for transmission, also starting with the preamble and ending with the CRC. The
MAC layer also generates jam data and transmits it to the PHY.
7.3.3 BUFFERED DMA INTERFACE (BDI)
The buffered DMA interface (BDI) supports read and write operations across the system bus. Two eight-bit buses
transfer data with optional parity checking. The system interface initiates data transfers. The MAC-layer controller
responds with a ready signal to accept data for transmission, or to deliver data which has been received. An end-
of-frame signal indicates the boundary between packets.
7.3.4 THE MAC TRANSMITTER BLOCK
The MAC transmitter block is responsible for transmitting data. It complies with the IEEE802.3 standard for the
carrier sense multiple access with collision detection (CSMA/CD) protocol.
7.3.4.1 MAC TxFIFO(MTxFIFO)
The MTxFIFO has an 80-byte depth. An extra bit is associated with each data byte for parity checking. This
80-byte by 9-bit size allows the first 64 bytes of a data frame to be stored and retransmitted, without further
system involvement, in case of a collision. If no collision occurs and transmission is underway, the additional 16
bytes handle system latency and avoid FIFO under-run.
When the system interface has set the MACTXCON.0 bit, the transmission state machine requests data from the
BDI. The system controller then fetches data from the system memory.
The data is stored in the MTxFIFO until the threshold for transmit data is satisfied. When the MTxFIFO is not full,
a request is issued to the BDI for more data. It then appends the calculated CRC to the end of the data (unless
the CRC truncate bit in the transmit control register is set).
7.3.4.2 Preamble and Jam Generator
As soon as the MACTXCON.0 bit is set and there are eight bytes of data in the MTxFIFO, the transmission state
machine starts the transmission by asserting the TX_EN signal and transmitting the preamble and the start frame
delimiter (SFD). In case there is a collision, it transmits a 32-bit string of `1’s after the preamble as a jam pattern.
7.3.4.3 PAD Generator
If a short data frame is transmitted, the MAC will normally generate pad bytes to extend the frame to a minimum
of 64 bytes. The pad bytes consist entirely of ‘0’ bits. A control bit is also used to suppress the generation of pad
bytes.
7.3.4.4 Parallel CRC Generator
The CRC generation of the outgoing data starts from the destination address and continues through the data
field. You can suppress CRC generation by setting the appropriate bit in the transmit control register. This is
useful in testing, for example, to force the transmission of a bad CRC in order to test error detection in the
receiver. It can also be useful in certain bridge or switch applications, where end-to-end CRC checking is desired.
Summary of Contents for S3C2500B
Page 2: ...S3C2500B 32 BIT RISC MICROPROCESSOR USER S MANUAL Revision 1 ...
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Page 80: ...PRODUCT OVERVIEW S3C2500B 1 46 NOTES ...
Page 296: ...MEMORY CONTROLLER S3C2500B 5 60 NOTES ...
Page 531: ...GDMA CONTROLLER S3C2500B 12 24 NOTES ...
Page 593: ...I O PORTS S3C2500B 15 12 NOTES ...