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Fast Ethernet Controllers (FEC0 and FEC1)
26-37
Freescale Semiconductor
The 7-wire serial mode interface (RCR
n
[MII_MODE] cleared and RCR [RMII_MODE] cleared or set)
is generally referred to as AMD mode.
shows the 7-wire mode connections to the external
transceiver.
26.5.7
FEC Frame Transmission
The Ethernet transmitter is designed to work with almost no intervention from software. After
ECR
n
[ETHER_EN] is set and data appears in the transmit FIFO, the Ethernet MAC can transmit onto the
network. The Ethernet controller transmits bytes least significant bit (lsb) first.
When the transmit FIFO fills to the watermark (defined by TFWR
n
), MAC transmit logic asserts
FEC
n
_TXEN and starts 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
n
_CRS is asserted). Before transmitting, the controller waits for carrier sense to become
inactive, then determines if carrier sense stays inactive for 60 bit times. If so, transmission begins after
waiting an additional 36 bit times (96 bit times after carrier sense originally became inactive). See
Section 26.5.17.1, “Transmission Errors,”
for more details.
Table 26-36. RMII Mode Configuration
Signal Description
EMAC Pin
Reference Clock
FEC
n
_
TXCLK
Transmit Enable
FEC
n
_
TXEN
Transmit Data
FEC
n
_
TXD[1:0]
Receive Data Valid
FEC
n
_
RXDV
Receive Data
FEC
n
_
RXD[1:0]
Receive Error
FEC
n
_RXER
Table 26-37. 7-Wire Mode Configuration
Signal description
EMAC Pin
Transmit Clock
FEC
n
_
TXCLK
Transmit Enable
FEC
n
_
TXEN
Transmit Data
FEC
n
_
TXD[0]
Collision
FEC
n
_
COL
Receive Clock
FEC
n
_
RXCLK
Receive Data Valid
FEC
n
_
RXDV
Receive Data
FEC
n
_
RXD[0]
n
Содержание MCF54455
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