W89C840F
The following table shows the group mapping relationship between the groups and the contents
of C38/CMA0 and C3C/CMA1. It is obviously shown that each bit in the registers C38/CMA0 and
C3C/CMA1 represents one group.
Bit 31~ 24
Bit 23 ~ 16
Group 24 ~ 17
Group 56 ~ 49
Bit 15 ~ 8
Group 16 ~ 9
Group 48 ~ 40
Bit 7 ~ 0
Group 8 ~ 1
Group 39 ~ 33
C38/CMA0
C3C/CMA1
Group 32 ~ 25
Group 64 ~ 57
All the 48 bits destination address (including physical address, multicast address and broadcast
address) of the incoming packet will be fed into the CRC generating mechanism. The six most
significant bits of the CRC (CRC31, CRC30, ... CRC26) will determine t o which group t he
i ncomi ng packet bel ongs. The relationship among these six bits of CRC content and the group that
the multicast address belongs to is shown as the following table.
CRC
31,30,29
000
CRC28,27,26
111
grp 8
110
101
100
011
010
001
000
grp 1
grp 7
grp 6
grp 5
grp 4
grp 3
grp 2
001
grp 16
grp 24
grp 32
grp 40
grp 48
grp 56
grp 64
grp 15 grp 14
grp 23 grp 22
grp 31 grp 30
grp 39 grp 38
grp 47 grp 46
grp 55 grp 54
grp 63 grp 62
grp 13
grp 21
grp 29
grp 37
grp 45
grp 53
grp 61
grp 12
grp 20
grp 28
grp 36
grp 44
grp 52
grp 60
grp 11
grp 19
grp 27
grp 35
grp 43
grp 51
grp 59
grp 10
grp 18
grp 26
grp 34
grp 42
grp 50
grp 58
grp 9
010
grp 17
grp 25
grp 33
grp 41
grp 49
grp 57
011
100
101
110
111
A packet with multicast address which belongs to the nth group will be accepted if the relative
bit of the nth group in C38/CMA0 and C3C/CMA1 is set to high and the bit 4 of C18/CNCR is also set
to high.
Besides the address recognition function, the MAC also performs the frame check sequence
validation function. Each incoming packet data, including the destination address, source address, the
packet data and the 4 bytes CRC data will be fed into the MAC s CRC generating logic to generate a 4
bytes CRC sequence. The MAC will compare this new CRC data with the one, included in the incoming
packet. It will be recognized as an error packet if these two 4-byte CRC data is not the same, but the bit
7 of C18/CNCR will determine if the MAC accepts the error packet or not. A high value of this bit will
force MAC to accept the error packet, and low to reject. An incoming packet without byte alignment
will be treated as an error packet. Some packets with the length less than 64 bytes caused by the
collision event on the network are also treated as an error packet. The terminology for the packet with
the length less than 64 bytes is called as runt packet. The extra control bit for accepting the runt packet
is defined as the bit 6 of C18/CNCR. To accept a runt packet, both of the bit 6 and bit 7 of C18/CNCR
should be set to high.
Publication Release Date:April 1997
- 19 -
Revision A1
ETC [ ETC ]
