MPC8280 datasheet(798/1386 Pages) FREESCALE

798 / 1386 page

SCC Ethernet Mode

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

25-10

Freescale Semiconductor

Table 25-3 describes receive commands.

NOTE

After a CPM reset via CPCR[RST], the Ethernet transmit enable (TENA)

signal defaults to its RTS, active-low functionality. To prevent false TENA

assertions to an external transceiver, configure TENA as an input before

issuing a CPM reset. See step 3 in Section 25.21, “SCC Ethernet

Programming Example.”

Table 25-2. Transmit Commands

Command

Description

STOP

TRANSMIT

When used with the Ethernet controller, this command violates a specific behavior of an Ethernet/IEEE

802.3 station. It should not be used.

GRACEFUL

STOP

TRANSMIT

Used to ensure that transmission stops smoothly after the current frame finishes or has a collision.

SCCE[GRA] is set once transmission stops, at which point Ethernet transmit parameters and their BDs

can be updated. TBPTR points to the next TxBD. Transmission begins once the R bit of the next BD is

set and a RESTART TRANSMIT command is issued.

Note that if GRACEFUL STOP TRANSMIT is issued and the current frame ends in a collision, TBPTR points

to the start of the collided frame with the R bit still set in the BD. The frame looks as if it was never sent.

RESTART

TRANSMIT

Enables transmission of characters on the transmit channel. The Ethernet controller expects it after a

GRACEFUL STOP TRANSMIT

command is issued or a transmitter error. The Ethernet controller resumes

transmission from the current TBPTR in the channel TxBD table.

INIT TX

PARAMETERS

Initializes transmit parameters in this serial channel parameter RAM to reset state. Issue only when the

transmitter is disabled. INIT TX and RX PARAMETERS resets both transmit and receive parameters.

Table 25-3. Receive Commands

Command

Description

ENTER HUNT

MODE

After hardware or software is reset and the channel is enabled in GSMR_L, the channel is in receive

enable mode and uses the first BD in the table. The receiver then enters hunt mode, waiting for an

incoming frame. The ENTER HUNT MODE command is generally used to force the Ethernet receiver to

stop receiving the current frame and enter hunt mode, in which the Ethernet controller continually scans

the input data stream for a transition of carrier sense from inactive to active and then a preamble

sequence followed by the start frame delimiter. After receiving the command, the buffer is closed and

the CRC calculation is reset. The next RxBD is used to receive more frames.

CLOSE RXBD

Should not be used with the Ethernet controller.

INIT RX

PARAMETERS

Initializes receive parameters in this serial channel parameter RAM to their reset state. Issue it only

when the receiver is disabled. INIT TX and RX PARAMETERS resets receive and transmit parameters.

SET GROUP

ADDRESS

Used to set one of the 64 bits of the four individual/group address hash filter registers. The address to

be added to the hash table should be written to TADDR_L, TADDR_M, and TADDR_H in the parameter

RAM before executing this command. The CP uses an individual address if the I/G bit in the address

stored in TADDR is 0; otherwise, it uses a group address. This command can be executed at any time,

regardless of whether the Ethernet channel is enabled.

To delete an address from the hash table, disable the Ethernet channel, clear the hash table registers,

and execute this command for the remaining addresses. Do not simply clear the channel’s associated

hash table bit because the hash table may have multiple addresses mapped to the same hash table bit.

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