8104 datasheet(39/172 Pages) LSI

39 / 172 page

Receive MAC

2-21

Undersize packets are packets whose length is less than the minimum

packet size. Minimum packet size is deﬁned to be 64 bytes, exclusive of

preamble and SFD. If a received packet is an undersize packet, the

frame is determined to be invalid and is discarded. Refer to Section 2.13,

“Packet Discard” for more information about discards. Clearing the

DIS_USIZE bit in “Register 8–Conﬁguration 2‚" Section 4.3.9, programs

the controller not to discard an undersize packet.

2.8.8 Maximum Packet Size

The maximum packet size used for receive MAC frame validity checking

is programmed to be one of four values, 1518, 1522, 1535 or unlimited

bytes. Setting the RMXPKT[1:0] receive MAC maximum packet size

select bits in “Register 9–Conﬁguration 3‚" Section 4.3.10, and the

DIS_OSIZE bit in “Register 8–Conﬁguration 2‚" Section 4.3.9, as shown

in Table 2.6. programs the controller to discard packets that exceed the

maximum packet size selected. This selection is also described in the

The bits shown in Table 2.6 affect the receive MAC section only; the

maximum packet size for the management counters is described in

Section 2.19, “Counters”.

2.8.9 MAC Control Frame Check

The length/type ﬁeld is checked to detect whether the packet is a valid

MAC control frame. Refer to Section 2.17, “MAC Control Frames” for

more details on MAC control frames.

Table 2.6

Receive Maximum Packet Size Selection

DIS_OSIZE Bit

RMXPKT [1:0] Bits

Maximum

Packet Size (Bytes)

0b0

xx1

1. xx = Don’t Care

unlimited

0b1

0b10

1535

0b1

0b01

1522

0b1

0b00

1518

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