Communication Processor Module
MOTOROLA
MPC823e REFERENCE MANUAL
16-329
COMMUNICATION
16
PROCESSOR MODULE
SCCs
• TBUF0_CRC—For internal use only.
• TBUF0_BCNT—For internal use only.
• PADDR1—You must write the 48-bit individual address of the station into this location.
PADDR1_L is the lowest order half-word, PADDR1_H is the highest order half-word
and PADDR_M is the middle half-word.
• P_PER—This parameter allows the SCCx Ethernet controller to be less aggressive
after a collision. Normally, this parameter is set to 0x0000. To decrease the
aggressiveness of the SCCx Ethernet controller, you can set P_PER to a value
between 1 (most aggressive) and 9 (least aggressive). The P_PER value is added to
the retry count in the backoff algorithm to reduce the probability of transmission on the
next time slot.
• RFBD_PTR—For internal use only. This register contains the first RX buffer descriptor
pointer.
• TFBD_PTR—For internal use only. This register contains the first TX buffer descriptor
pointer.
• TLBD_PTR—For internal use only. This register contains the last TX buffer descriptor
pointer.
• TX_LEN—For internal use only.
• IADDR1–4 —These four registers are used in the hash table function of the individual
addressing mode. You can write zeros to these values after reset and before the
Ethernet channel is enabled to disable all individual hash address recognition functions.
The
SET GROUP ADDRESS
command is used to enable the hash table.
• BOFF_CNT—For internal use only.
• TADDR—This parameter allows you to add and delete addresses from the individual
and group hash tables. After placing an address in TADDR, you must issue the
SET
GROUP ADDRESS
command. TADDR_L is the lowest order half-word, TADDR_H is
the highest order half-word and TADDR_M is the middle half-word.
Note:
The Ethernet/802.3 specification allows the use of P_PER. In a heavily
congested Ethernet LAN, a less aggressive backoff algorithm used by multiple
stations on the LAN increases the overall LAN throughput by reducing the
probability of collisions. The SBT bit in the PSMR–SCC Ethernet offers another
way to reduce the aggressiveness of the SCCx Ethernet controller.
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