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Communication Processor Module
• MFLR—The SCCx Ethernet controller checks the length of an incoming Ethernet frame
against the user-defined value given in this 16-bit register. Typically this register is set
to 0x5EE. If this limit is exceeded, the remainder of the incoming frame is discarded and
the LG bit is set in the last RX buffer descriptor belonging to that frame. The SCCx
Ethernet controller reports the frame status and length in the last RX buffer descriptor.
MFLR is defined as all the in-frame bytes between the start frame delimiter and the end
of the frame.
• MINFLR—The SCCx Ethernet controller checks the length of an incoming Ethernet
frame against the user-defined value given in this 16-bit register that is typically set to
0x40. If the received frame length is less than the register value, then this frame is
discarded, unless the RSH bit in the PSMR–SCC Ethernet is set. If RSH is set, then the
SH bit is set in the last RX buffer descriptor belonging to that frame. For transmit
operation when the frame is too short, the SCCx Ethernet controller adds PADs to the
transmitted frame, depending on how the PAD bit is set in the TX buffer descriptor and
the PAD value in the parameter RAM. Pad characters are added to make the transmit
frame MINFLR bytes in length.
• MAXD1—This parameter gives you the option to stop system bus writes from occurring
after a frame has exceeded a certain size. However, the value of this register is valid
only if an address match is found. The SCCx Ethernet controller checks the length of
an incoming Ethernet frame against the user-defined value given in this 16-bit register
that is usually set to 0x5F0. If this limit is exceeded, the remainder of the incoming frame
is discarded. The SCCx Ethernet controller waits until the end of the frame is reached
or until the MFLR bytes have been received and then it reports the frame status and
length in the last RX buffer descriptor.
• MAXD2—This parameter also gives you the option to stop system bus writes from
occurring after a frame has exceeded a certain size. However, the value of this register
is valid in promiscuous mode when no address match is detected. The SCCx Ethernet
controller checks the length of an incoming Ethernet frame against the user-defined
value given in this 16-bit register that is usually set to 0x5F0. If this limit is exceeded,
the remainder of the incoming frame is discarded. The SCCx Ethernet controller waits
until the end of the frame is reached or until the MFLR bytes have been received and
then it reports the frame status and length in the last RX buffer descriptor. In a monitor
station, MAXD2 can be programmed to a value much less than MAXD1 to receive entire
frames addressed to this station, but receives only the headers of the other frames.
• MAXD—For internal use only.
• MAX_B—For internal use only.
• DMA_CNT is a temporary down-counter used to track the frame length.
• GADDR1–4—These four registers are used in the hash table function of the group
addressing mode. You can write zeros to these values after reset and before the
Ethernet channel is enabled to disable all group hash address recognition functions.
The SET GROUP ADDRESS command is used to enable the hash table.
• TBUF0_DATA0—For internal use only.
• TBUF0_DATA1—For internal use only.
• TBUF0_RBA0—For internal use only.
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MPC823e REFERENCE MANUAL
MOTOROLA
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