Motorola MPC860 PowerQUICC User Manual page 750

Part V. The Communications Processor Module
a random period of time, called a backoff, before trying to retransmit. Once the backoff time
expires, the station waits for silence on the LAN before retransmitting, which is called a
retry. If the frame cannot be sent within 15 retries, an error occurs
10-Mbps Ethernet transmits at 0.8 ms per byte. The preamble plus start frame delimiter is
sent in 6.4 ms. The minimum 10-Mbps Ethernet interframe gap is 9.6 ms and the slot time
is 52 ms.
28.1 Ethernet on the MPC860
Setting GSMR[MODE] to 0b1100 selects Ethernet. The SCC performs the full set of IEEE
802.3/Ethernet CSMA/CD media access control and channel interface functions.
U-BUS
PERIPHERAL BUS
REJECT
RECEIVER
RSTRT
CONTROL
CD = RENA
CTS = CLSN
RXD
The MPC860 Ethernet controller requires an external serial interface adaptor (SIA) and
transceiver function to complete the interface to the media. This function is implemented
in the Motorola MC68160 enhanced Ethernet serial transceiver (EEST).
The MPC860+EEST solution provides a direct connection to the attachment unit interface
(AUI) or twisted-pair (10BASE-T). The EEST provides a glueless interface to the MPC860,
Manchester encoding and decoding, automatic selection of 10BASE-T versus AUI ports,
10BASE-T polarity detection and correction. The MC68160 documentation gives more
information.
Although the MPC860 contains DPLLs that allow Manchester encoding and decoding,
these DPLLs were not designed for Ethernet rates. Therefore, the MPC860 Ethernet
controller bypasses the on-chip DPLLs and uses the external system interface adaptor on
28-2
CONTROL
REGISTERS
RX
DATA
UNIT FIFO
SHIFTER
Figure 28-2. Ethernet Block Diagram
MPC860 PowerQUICC UserÕs Manual
INTERNAL CLOCKS
TX
TRANSMITTER
DATA
CONTROL
FIFO
UNIT
TXD
SHIFTER
SLOT TIME
AND DEFER
COUNTER
RCLK
CLOCK
GENERATOR
TCLK
RTS = TENA
CD = RENA
CTS = CLSN
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