8101 datasheet(35/172 Pages) LSI

35 / 172 page

Receive MAC

2-17

2.7.5 MAC Control Frame Generation

The transmit MAC can automatically generate and transmit MAC control

pause frames, which are used for ﬂow control. This function is described

in more detail in Section 2.17, “MAC Control Frames”.

2.8 Receive MAC

The receive MAC section performs the following operations to

disassemble Ethernet packets received from the receive 8B10B PCS

section:

• Strips off the preamble and SFD

• Strips off the CRC

• Checks the destination address against the address ﬁlters to

determine packet validity

• Checks frame validity against the discard conditions

• Checks the length/type ﬁeld for MAC control frames

Each of the above operations can be individually disabled and altered, if

desired. The receive MAC then sends valid packets to the receive FIFO

for storage.

2.8.1 Preamble and SFD Stripping

The transmit MAC normally strips the preamble and SFD from the

receive packet. To program the controller to not strip the preamble and

SFD set the RXPRMBL bit in “Register 7–Conﬁguration 1‚" Section 4.3.8.

When this bit is set, the preamble and SFD are left in the receive packet

and are stored in the receive FIFO as a part of the packet.

2.8.2 CRC Stripping

The receive MAC normally strips the FCS from the receive packet. To

program the controller to not strip the FCS ﬁeld, set the RXCRC bit in

“Register 7–Conﬁguration 1‚" Section 4.3.8. When this bit is set the last

four bytes of the packet containing the CRC value are left in the receive

packet and are stored in the receive FIFO as part of the packet.

8101 Datasheet(PDF) 35 Page - LSI Computer Systems