![Freescale Semiconductor MCF52230 ColdFire Скачать руководство пользователя страница 276](http://html1.mh-extra.com/html/freescale-semiconductor/mcf52230-coldfire/mcf52230-coldfire_reference-manual_2330648276.webp)
Fast Ethernet Controller (FEC)
MCF52235 ColdFire® Integrated Microcontroller Reference Manual, Rev. 6
Freescale Semiconductor
18-7
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
.
18.4.6
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 asserts
ETXEN 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
(ECRS 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
” 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 is appended to the frame data regardless of
Receive Error
ERXER
Management Data Clock
EMDC
Management Data
Input/Output
EMDIO
Table 18-6. 7-Wire Mode Configuration
Signal description
EMAC Pin
Transmit Clock
ETXCLK
Transmit Enable
ETXEN
Transmit Data
ETXD[0]
Collision
ECOL
Receive Clock
ERXCLK
Receive Data Valid
ERXDV
Receive Data
ERXD[0]
Table 18-5. MII Mode (continued)
Signal Description
EMAC pin
Because
of
an
order
from
the
United
States
International
Trade
Commission,
BGA-packaged
product
lines
and
part
numbers
indicated
here
currently
are
not
available
from
Freescale
for
import
or
sale
in
the
United
States
prior
to
September
2010:MCF52234CVM60,
MCF52235CVM60