MPC5553/MPC5554 Microcontroller Reference Manual, Rev. 5
Freescale Semiconductor
14-37
The 7-wire serial mode interface (RCR[MII_MODE] = 0) operates in what is generally referred to as the
“AMD” mode. 7-wire mode connections to the external transceiver are shown in
.
14.4.6
FEC Frame Transmission
The Ethernet transmitter is designed to work with almost no intervention from software. After
ECR[ETHER_EN] is asserted and data appears in the transmit FIFO, the Ethernet MAC is able to transmit
onto the network.
When the transmit FIFO fills to the watermark (defined by the TFWR), the MAC transmit logic will assert
FEC_TX_EN and start transmitting the preamble (PA) sequence, the start frame delimiter (SFD), and then
the frame information from the FIFO. However, the controller defers the transmission if the network is
busy (FEC_CRS asserts). Before transmitting, the controller waits for carrier sense to become inactive,
then determines if carrier sense stays inactive for 60 bit times. If so, the transmission begins after waiting
an additional 36 bit times (96 bit times after carrier sense originally became inactive). See
Section 14.4.14.1, “Transmission Errors
” for more details.
If a collision occurs during transmission of the frame (half-duplex mode), the Ethernet controller follows
the specified backoff procedures and attempts to retransmit the frame until the retry limit is reached. The
transmit FIFO stores at least the first 64 bytes of the transmit frame, so that they do not have to be retrieved
from system memory in case of a collision. This improves bus utilization and latency in case immediate
retransmission is necessary.
When all the frame data has been transmitted, the FCS (frame check sequence or 32-bit cyclic redundancy
check, CRC) bytes are appended if the TC bit is set in the transmit frame control word. If the ABC bit is
set in the transmit frame control word, a bad CRC will be appended to the frame data regardless of the TC
bit value. Following the transmission of the CRC, the Ethernet controller writes the frame status
information to the MIB block. Short frames are automatically padded by the transmit logic (if the TC bit
in the transmit buffer descriptor for the end of frame buffer = 1).
Management Data Clock
FEC_MDC
Management Data
Input/Output
FEC_MDIO
Table 14-34. 7-Wire Mode Configuration
Signal Description
FEC Signal
Transmit Clock
FEC_CLK
Transmit Enable
FEC_TX_EN
Transmit Data
FEC_TXD0
Collision
FEC_COL
Receive Clock
FEC_RX_CLK
Receive Data Valid
FEC_RX_DV
Receive Data
FEC_RX_D0
Table 14-33. MII Mode (Continued)
Signal Description
EMAC Signal
Summary of Contents for MPC5553
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