Motorola MPC823e Reference Manual page 785

• GRACEFUL STOP TRANSMIT —This command is used to ensure that transmission
stops smoothly after the current frame finishes or undergoes a collision. The GRA bit in
the SCCE–Ethernet register is set once transmission stops. Then you can modify the
Ethernet transmit parameters and their buffer descriptors. The TBPTR points to the
next TX buffer descriptor in the table. Transmission begins once the R bit of the next
buffer descriptor is set and the RESTART TRANSMIT command is issued.
Note: If the GRACEFUL STOP TRANSMIT command is issued and the current
transmit frame ends in a collision, the TBPTR points to the beginning of the
collided frame with the R bit still set in the TX buffer descriptor. The frame will
look as if it was never transmitted.
• RESTART TRANSMIT —This command enables the transmission of characters on the
transmit channel. The SCCx Ethernet controller expects it after a GRACEFUL STOP
TRANSMIT command is issued or a transmitter error occurs. The SCCx Ethernet
controller resumes transmission from the current TBPTR in the channel TX buffer
descriptor table.
• INIT TX PARAMETERS—This command initializes all the transmit parameters in this
serial channel parameter RAM to their reset state. It must only be issued when the
transmitter is disabled. The INIT TX AND RX PARAMS command can also be used to
reset the transmit and receive parameters.
You can program the CPM command register with the following commands to receive data.
See Section 16.2.6.1 CPM Command Register for additional information.
• ENTER HUNT MODE—After the hardware or software is reset and the channel in the
SCCM–Ethernet register is enabled, the channel is in receive enable mode and uses
the first buffer descriptor in the table. This command is generally used to force the
Ethernet receiver to stop receiving the current frame and enter hunt mode. In this mode,
the SCCx Ethernet controller continually scans the input datastream 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 current receive buffer is closed and
the CRC calculation is reset. The next RX buffer descriptor is used to receive more
frames.
• CLOSE RX BD—This command must not be used when a serial communication
controller is in Ethernet mode.
• INIT RX PARAMETERS—This command initializes all the receive parameters in this
serial channel parameter RAM to their reset state and must only be issued when the
receiver is disabled. The INIT TX AND RX PARAMS command can also be used to
reset the receive and transmit parameters.
MOTOROLA MPC823e REFERENCE MANUAL
Communication Processor Module
16-331