PM3350 ELAN 8 X10
ELAN 8X10
DATA SHEET
PMC-970109
ISSUE 3
8 PORT ETHERNET SWITCH
expansion port. The DMA Coprocessor operates under the control of the Switch
Processor unit to transfer packets and data at high speed between the 10BaseT ports,
the local memory and the expansion port. It also computes 32-bit IEEE Frame Check
Sequence (FCS) CRC remainders over the transferred data, allowing the Switch
Processor to filter packets with errors and generate CRCs for transmitted packets as
required.
Ethernet/IEEE 802.3 MAC Interfaces
Eight independent Ethernet/IEEE 802.3 MAC-layer interfaces are built into the ELAN
8x10 chip. These interfaces connect directly to external 10BaseT Medium Access Unit
(MAU) devices via the industry-standard 7-wire serial interface, and perform most of the
MAC-layer processing tasks required for CSMA/CD networks. In addition, each MAC
interface contains a 32-byte FIFO buffer that enhances throughput and minimizes
latency issues.
The signaling protocol used on the 7-wire serial interfaces supported by the ELAN 8x10
chip follows that required by the Advanced Micro Devices, Inc (AMD) Am7990 LANCE
device.
Expansion Port
A 32-bit parity-checked expansion port is provided to allow systems using the ELAN
8x10 to be expanded transparently from 8 to 64 ports. The expansion port supports a
peak throughput of 1 Gbit/s, and requires only a single external PAL or similar device
(to serve as a bus arbiter). Packets received on an ELAN 8x10 MAC port that are
destined for an external ELAN 8x10 are transferred over the expansion bus prior to
transmission on the designated destination port. Broadcast and multicast packets are
handled using a two-level replication scheme, in which the broadcast/multicast packet is
first transferred to all of the external ELAN 8x10s, after which it is transmitted out the
required destination ports without any further use of the expansion bus. In addition,
ELAN 8x10s interconnected via the expansion port exchange information to maintain
the distributed MIB.
Local Memory Controller
An external local memory is used for holding configuration information, MAC address
tables and statistics tables, node management data, packet buffers, and host
communication queues (if a local host CPU is present). The ELAN 8x10 integrates a
memory controller that is capable of addressing and directly driving up to 16 Mbytes of
external memory, divided into four banks of 4 Mbytes each, with decoded selects for
each bank. Independent, software programmable access times may be set for each
bank, allowing a glueless interface to a mix of EDO DRAM, EEPROM, EPROM and
ROM in the same system. An external memory timing generator may also be used if
desired. The memory controller accepts simultaneous requests from the Switch
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10
PMC [ PMC-SIERRA, INC ]
