dp83902a National Semiconductor Corporation, dp83902a Datasheet - Page 36

• Manufacturer Part Number: dp83902a
• Description: St-nictm Serial Network Interface Controller For Twisted Pair
• Manufacturer: National Semiconductor Corporation

10 0 Internal Registers
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
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
MAR0 FB7
MAR1 FB15 FB14 FB13 FB12 FB11 FB10 FB9
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
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
D7
FB6
D6
FB5
D5
FB4
D4
FB3
D3
(Continued)
FB2
D2
TL F 11157 – 53
FB1
D1
FB0
FB8
D0
36
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
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
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
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
Note The FIFO should only be read when the ST-NIC has been pro-
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
CNTR0 CT7 CT6 CT5 CT4 CT3 CT2 CT1 CT0
CNTR1 CT7 CT6 CT5 CT4 CT3 CT2 CT1 CT0
CNTR2 CT7 CT6 CT5 CT4 CT3 CT2 CT1 CT0
FIFO DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0
NCR
grammed in loopback mode
7
7
7
7
7
6
6
6
6
6
5
5
5
5
5
4
4
4
4
4
NC3 NC2 NC1 NC0
3
3
3
3
3
2
2
2
2
2
1
1
1
1
1
0
0
0
0
0