Ethernet On The Mpc8260 - Motorola MPC8260 PowerQUICC II User Manual

Part IV. 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 µs per byte. The preamble plus start frame delimiter is
sent in 6.4 µs. The minimum 10-Mbps Ethernet interframe gap is 9.6 µs and the slot time
is 52 µs.

24.1 Ethernet on the MPC8260

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.
60x Bus
Peripheral Bus
REJECT
Receiver
RSTRT
CD = RENA
CTS = CLSN
RXD
The MPC8260 Ethernet controller requires an external serial interface adaptor (SIA) and
transceiver function to complete the interface to the media.
Although the MPC8260 contains DPLLs that allow Manchester encoding and decoding,
these DPLLs were not designed for Ethernet rates. Therefore, the MPC8260 Ethernet
controller bypasses the on-chip DPLLs and uses the external system interface adaptor on
the EEST instead. The on-chip DPLL cannot be used for low-speed (1-Mbps) Ethernet
either because it cannot properly detect start-of-frame or end-of-frame.
Note that the CPM of the MPC8260 requires a minimum system clock frequency of 24
MHz to support Ethernet.
24-2
Control
Registers
Rx
Control Data
Unit FIFO
Shifter
Figure 24-2. Ethernet Block Diagram
MPC8260 PowerQUICC II 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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