W89C840F
The MAC also performs many other transmission functions specified by the IEEE802.3,
including the inter-frame spacing function, collision detection, collision enforcement, collision backoff
and re-transmission. The collision backoff timer is a function of the integer slot time, 512 bit times. The
number of slot times to delay between the current transmission attempt to the next attempt is determined
by a uniformly distributed random integer algorithm specified by the IEEE802.3. The integer, r, is
specified as the following
0 £ r £ 2k
where k = min.(n, 10)
The MAC performs the receive functions specified by the IEEE802.3 including the address
recognition function, the frame check sequence validation, the frame disassembly, framing and collision
filtering.
The W89C840F categorizes the input stream from media into three types of frame. These three
types are the packet with unicast destination address, the multicast destination address and the broadcast
destination address. A unicast address is defined as a destination address with its first bit(the LSB) low.
A multicast address is defined as a destination address with its first bit(the LSB) high but the other 47
bits are not all one. A broadcast address is defined as a destination address with its all 48 bits are one.
All the three t ypes of t he packet r ecept i on ar e selectively determined by the configuration of
the bit 3, 4 and 5 of the C18/CNCR register of the W89C840F.
The C40/CPA0 and C44/CPA1 are used to store your own 48 bits Ethernet ID of the network
node before starting to receive a packet. I t s cont ent s come from EEPROM after power-on reset.
The mapping relationship among the 48 bits ID and the C40/CPA0 and C44/CPA1 are as
following table.
Bit 31~ 24
32nd ~ 25th
reserved
Bit 23 ~ 16
24th ~ 17th
reserved
Bit 15 ~ 8
16th ~ 9th
48th ~ 41st
Bit 7 ~ 0
8th ~ 1st
C40/CPA0
C44/CPA1
40th ~ 33rd
The incoming packet with unicast address will be accepted if the bit 3 of C18/CNCR is reset to
low and the destination address of the incoming unicast packet has to match with the content of
C40/CPA0 and C44/CPA1 setting.
All of the incoming packet with unicast address will be accepted if the bit 3 of C18/CNCR is set
to high.
In broadcast case, to accept a packet with a broadcast destination address, the bit 5 of C18/CNCR
must be set to high. Otherwise, the W89C840F will reject this broadcast packet.
In multicast case, a packet with a multicast destination address will be accepted if the destination
address is grouped into the selected group specified by the registers of C38/CMA0 and C3C/CMA1.
These two registers are used to store the group mapping for the multicast packet.
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ETC [ ETC ]
