SAM3X8C Atmel Corporation, SAM3X8C Datasheet - Page 1274

• Manufacturer Part Number: SAM3X8C
• Manufacturer: Atmel Corporation

41.4.6
1274
1274
SAM3X/A
SAM3X/A
Address Checking Block
The address checking (or filter) block indicates to the DMA block which receive frames should
be copied to memory. Whether a frame is copied depends on what is enabled in the network
configuration register, the state of the external match pin, the contents of the specific address
and hash registers and the frame’s destination address. In this implementation of the EMAC, the
frame’s source address is not checked. Provided that bit 18 of the Network Configuration regis-
ter is not set, a frame is not copied to memory if the EMAC is transmitting in half duplex mode at
the time a destination address is received. If bit 18 of the Network Configuration register is set,
frames can be received while transmitting in half-duplex mode.
Ethernet frames are transmitted a byte at a time, least significant bit first. The first six bytes (48
bits) of an Ethernet frame make up the destination address. The first bit of the destination
address, the LSB of the first byte of the frame, is the group/individual bit: this is One for multicast
addresses and Zero for unicast. The All Ones address is the broadcast address, and a special
case of multicast.
The EMAC supports recognition of four specific addresses. Each specific address requires two
registers, specific address register bottom and specific address register top. Specific address
register bottom stores the first four bytes of the destination address and specific address register
top contains the last two bytes. The addresses stored can be specific, group, local or universal.
The destination address of received frames is compared against the data stored in the specific
address registers once they have been activated. The addresses are deactivated at reset or
when their corresponding specific address register bottom is written. They are activated when
specific address register top is written. If a receive frame address matches an active address,
the frame is copied to memory.
The following example illustrates the use of the address match registers for a MAC address of
21:43:65:87:A9:CB.
Preamble 55
SFD D5
DA (Octet0 - LSB) 21
DA(Octet 1) 43
DA(Octet 2) 65
DA(Octet 3) 87
DA(Octet 4) A9
DA (Octet5 - MSB) CB
SA (LSB) 00
SA 00
SA 00
SA 00
SA 00
SA (MSB) 43
SA (LSB) 21
11057A–ATARM–17-Feb-12
11057A–ATARM–17-Feb-12