AM79C90JCTR AMD [Advanced Micro Devices], AM79C90JCTR Datasheet - Page 10

• Manufacturer Part Number: AM79C90JCTR
• Description: CMOS Local Area Network Controller for Ethernet (C-LANCE)
• Manufacturer: AMD [Advanced Micro Devices]

under “Logical Address Filter.” The second logical ad-
dress is a broadcast address where all nodes on the net-
work receive the packet. The last receive mode of
operation is referred to as “promiscuous mode” in which
a node will accept all packets on the medium regardless
of their destination address.
Collision Detection and Implementation
The Ethernet and IEEE 802.3 CSMA/CD network ac-
cess algorithms are implemented completely within the
C-LANCE. In addition to listening for a clear medium be-
fore transmitting, Ethernet handles collisions in a prede-
termined way. Should two transmitters attempt to seize
the medium at the same time, they will collide and the
data on the medium will be garbled. The transmitting
nodes listen while they transmit, detect the collision,
then continue to transmit for a predetermined length of
time to “jam” the network and ensure that all nodes have
recognized the collision. The transmitting nodes then
delay a random amount of time according to the Ether-
net “truncated binary backoff” algorithm in order that the
colliding nodes do not try to repeatedly access the net-
work at the same time. The C-LANCE also offers a se-
lectable
performance on busy networks. Up to 16 attempts to ac-
cess the network are made by the C-LANCE before re-
porting an error due to excessive collisions.
Error Reporting and Diagnostics
Extensive error reporting is provided by the C-LANCE.
Error conditions reported relate either to the network as
a whole or to individual data packets. Network-related
errors are recorded as flags in the CSRs and are exam-
ined by the CPU following interrupt. Packet-related er-
rors are written into descriptor entries corresponding to
the packet.
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Am79C90
System errors include:
Packet-related errors:
The C-LANCE performs several diagnostic routines
which enhance the reliability and integrity of the system.
These include a CRC check and two loop back modes
(internal/external). Errors may be introduced into the
system to check error detection logic. A Time Domain
Reflectometer is incorporated into the C-LANCE to aid
system designers in locating faults in the Ethernet physi-
cal medium. Shorts and opens manifest themselves in
reflections which are sensed by the TDR.
Babbling Transmitter
— Transmitter attempting to transmit more than
Collision
— Collision detection circuitry nonfunctional
Missed Packet
— Insufficient buffer space
Memory timeout
— Memory response failure
CRC
— Invalid data
Framing
— Packet did not end on a byte boundary
— Indicates abnormal latency in servicing a DMA
Buffer
— Insufficient buffer space available
1518 bytes, excluding preamble and start frame
delimiter
Overflow/Underflow
request