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AM79C90PCTR Datasheet(PDF) 10 Page - Advanced Micro Devices |
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AM79C90PCTR Datasheet(HTML) 10 Page - Advanced Micro Devices |
10 / 62 page AMD P R E L I M I N A R Y 10 Am79C90 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 Modified Backoff Algorithm for better 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. System errors include: Babbling Transmitter — Transmitter attempting to transmit more than 1518 bytes, excluding preamble and start frame delimiter Collision — Collision detection circuitry nonfunctional Missed Packet — Insufficient buffer space Memory timeout — Memory response failure Packet-related errors: CRC — Invalid data Framing — Packet did not end on a byte boundary Overflow/Underflow — Indicates abnormal latency in servicing a DMA request Buffer — Insufficient buffer space available 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. |
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