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10.0 Internal Registers
(Continued)
cant bits of the CRC generator are latched. These 6 bits are
then decoded by a 1 of 64 decode to index a unique filter bit
(FB0 – 63) in the multicast address registers. If the filter bit
selected is set, the multicast packet is accepted. The sys-
tem designer would use a program to determine which filter
bits to set in the multicast registers. All multicast filter bits
that correspond to multicast address accepted by the node
are then set to one. To accept all multicast packets all of
the registers are set to all ones.
Note:
Although the hashing algorithm does not guarantee perfect filtering of
multicast address, it will perfectly filter up to 64 multicast addresses if
these addresses are chosen to map into unique locations in the multi-
cast filter.
TL/F/11157 – 53
D7
D6
D5
D4
D3
D2
D1
D0
MAR0 FB7
FB6
FB5
FB4
FB3
FB2
FB1
FB0
MAR1 FB15 FB14 FB13 FB12 FB11 FB10 FB9
FB8
MAR2 FB23 FB22 FB21 FB20 FB19 FB18 FB17 FB16
MAR3 FB31 FB30 FB29 FB28 FB27 FB26 FB25 FB24
MAR4 FB39 FB38 FB37 FB36 FB35 FB34 FB33 FB32
MAR5 FB47 FB46 FB45 FB44 FB43 FB42 FB41 FB40
MAR6 FB55 FB54 FB53 FB52 FB51 FB50 FB49 FB48
MAR7 FB63 FB62 FB61 FB60 FB59 FB58 FB57 FB56
If address Y is found to hash to the value 32 (20H), then
FB32 in MAR4 should be initialized to ‘‘1’’. This will cause
the ST-NIC to accept any multicast packet with the address
Y.
10.10 NETWORK TALLY COUNTERS
Three 8-bit counters are provided for monitoring the number
of CRC errors, Frame Alignment Errors and Missed Pack-
ets. The maximum count reached by any counter is 192
(C0H). These registers will be cleared when read by the
CPU. The count is recorded in binary in CT0 – CT7 of each
Tally Register.
Frame Alignment Error Tally (CNTR0)
This counter increments every time a packet is received
with a Frame Alignment Error. The packet must have been
recognized by the address recognition logic. The counter is
cleared after it is read by the processor.
7
6
5
4
3
2
1
0
CNTR0
CT7
CT6
CT5
CT4
CT3
CT2
CT1
CT0
CRC Error Tally (CNTR1)
This counter is incremented every time a packet is received
with a CRC error. The packet must first be recognized by
the address recognition logic. The counter is cleared after it
is read by the processor.
7
6
5
4
3
2
1
0
CNTR1
CT7
CT6
CT5
CT4
CT3
CT2
CT1
CT0
Frames Lost Tally Register (CNTR2)
This counter is incremented if a packet cannot be received
due to lack of buffer resources. In monitor mode, this coun-
ter will count the number of packets that pass the address
recognition logic.
7
6
5
4
3
2
1
0
CNTR2
CT7
CT6
CT5
CT4
CT3
CT2
CT1
CT0
FIFO
This is an 8-bit register that allows the CPU to examine the
contents of the FIFO after loopback. The FIFO will contain
the last 8 data bytes transmitted in the loopback packet.
Sequential reads from the FIFO will advance a pointer in the
FIFO and allow reading of all 8 bytes.
7
6
5
4
3
2
1
0
FIFO
DB7
DB6
DB5
DB4
DB3
DB2
DB1
DB0
Note:
The FIFO should only be read when the ST-NIC has been pro-
grammed in loopback mode.
NUMBER OF COLLISIONS (NCR)
This register contains the number of collisions a node expe-
riences when attempting to transmit a packet. If no colli-
sions are experienced during a transmission attempt, the
COL bit of the TSR will not be set and the contents of NCR
will be zero. If there are excessive collisions, the ABT bit in
the TSR will be set and the contents of NCR will be zero.
The NCR is cleared after the TXP bit in the CR is set.
7
6
5
4
3
2
1
0
NCR
Ð
Ð
Ð
Ð
NC3
NC2
NC1
NC0
36
Obsolete