SCC Ethernet Mode
MPC8260 PowerQUICC II Family Reference Manual, Rev. 2
25-8 Freescale Semiconductor
0x4C MINFLR Hword Minimum frame length register. The Ethernet controller checks the incoming
frame’s length against MINFLR (typically 64 decimal). If the received frame is
smaller than MINFLR, it is discarded unless PSMR[RSH] is set, in which case,
SH is set in the last BD for the frame. For transmitting a frame that is too short,
the Ethernet controller pads the frame to make it MINFLR bytes long, depending
on how PAD is set in the TxBD and on the PAD value in the parameter RAM.
0x4E MAXD1 Hword Max DMA
n
length register. Gives the option to stop system bus writes after a
frame exceeds a certain size. However, this value is valid only if an address
match is found. The Ethernet controller checks the length of an incoming Ethernet
frame against this user-defined value (usually 1520 decimal). If this limit is
exceeded, the rest of the incoming frame is discarded. The Ethernet controller
waits until the end of the frame or until MFLR bytes are received and reports the
frame status and the frame length in the last RxBD.
MAXD1 is used when an address matches an individual or group address.
MAXD2 is used in promiscuous mode when no address match is detected. In a
monitor station, MAXD2 can be much less than MAXD1 to receive entire frames
addressed to this station, but only the headers of the other frames are received.
0x50 MAXD2 Hword
0x52 MAXD Hword Rx max DMA.
0x54 DMA_CNT Hword Rx DMA counter. A temporary down-counter used to track frame length.
0x56 MAX_B Hword Maximum BD byte count.
0x58 GADDR1 Hword Group address filter 1–4. Used in the hash table function of the group addressing
mode. 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.
0x5A GADDR2
0x5C GADDR3
0x5E GADDR4
0x60 TBUF0_DATA0 Word Save area 0—current frame.
0x64 TBUF0_DATA1 Word Save area 1—current frame.
0x68 TBUF0_RBA0 Word
0x6C TBUF0_CRC Word
0x70 TBUF0_BCNT Hword
0x72 PADDR1_H Hword The 48-bit individual address of this station into this location. PADDR1_L is the
lowest order hword and PADDR1_H is the highest order hword.
0x74 PADDR1_M
0x76 PADDR1_L
0x78 P_PER Hword Persistence. Lets the Ethernet controller be less aggressive after a collision.
Normally, 0x0000. It can be a value between 1 and 9 (1 is most aggressive). The
value is added to the retry count in the backoff algorithm to reduce the chance of
transmission on the next time slot.
Note: Using P_PER is fully allowed in the Ethernet/802.3 specifications. A less
aggressive backoff algorithm used by multiple stations on a congested Ethernet
LAN increases overall throughput by reducing the chance of collision.
PSMR[SBT] offers another way to reduce the aggressiveness of the Ethernet
controller.
0x7A RFBD_PTR Hword Rx first BD pointer.
Table25 -1. SCC Ethernet Parameter RAM Memory Map (con tinued)
Offset 1Name Width Description