![](http://datasheet.mmic.net.cn/110000/GT-48208_datasheet_3491735/GT-48208_19.png)
GT-482xx Switched Ethernet Controllers for 10+10/100 BaseX
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3.
GALAXY FAMILY OVERVIEW
The Galaxy Family of switching devices is designed to provide the lowest cost solutions for desktop and work-
group Ethernet switching.
The Galaxy Family currently includes the following devices:
GT-48212
Twelve ports of 10BaseX, two ports of 100BaseX with management interface
GT-48208
Eight ports of 10BaseX, two ports of 100BaseX with management interface
GT-48207
Eight ports of 10BaseX, two ports of 100BaseX but without any management capability.
The GT-48207 is designed for cost-sensitive “hub replacement” applications.
During the design of the Galaxy Family, Galileo Technology had the following goals:
Produce a Product Yielding the Lowest Possible System Cost. This is evident in the Galaxy Family’s
high level of integration and lower overall bill-of-materials. For example, Galaxy Family devices do not
require the external address Lookup/VLAN engines and PHY devices required by other solutions. We
have also made it very simple to interface a CPU.
Make it Simple for the Switch OEM to Build a Modular/Flexible Product Line. The GT-48212, GT-
48208, and GT-48207 all share a common pinout. This allows the OEM to build a variety of port densities
and management options on the same printed circuit board. This flexibility allows the OEM to manage
production planning more effectively.
Provide Software Compatibility to Future Generations. Future generations of Galaxy devices that
support different port speeds/densities will strive for backwards software compatibility. This allows you to
write your management code once, and only modify it as your end-user requirements change.
Galileo Technology will continue to extend the Galaxy Family to meet future needs for workgroup/desktop LANs.
The Galaxy Family uses a “store-and-forward” switching approach. Store-and-forward was chosen for the follow-
ing reasons:
Store-and-forward switches allow switching between different speed media (e.g. 10BaseX and
100BaseX.) Such switches require the large elastic buffers that are provided by the SDRAM arrays.
Store-and-forward switches improve overall network performance by acting as a “network cache”, effec-
tively buffering packets during periods of heavy congestion.
Store-and-forward switches prevent the forwarding of corrupted packets by analyzing the frame check
sequence (FCS) before forwarding to the destination port.
3.1
Basic Operation
The basic operation of the GT-482xx is quite simple. The GT-482xx receives incoming packets from the Ethernet
wire, searches in the Address Table for the Destination MAC Address and then forwards the packet to the appro-
priate port. The destination port can either be local (one of the GT-482xx’s ports) or in a different GT-482xx device
that is connected via the Fast MII expansion bus. If the destination address is not found, the GT-482xx treats the
packet as a Multicast packet and forwards the packet to all ports of all the devices in the system specified to for-
ward unknown packets.
The GT-482xx automatically learns the port number of attached network devices by examining the Source MAC
Address of all incoming packets. If the Source Address is not found in the GT-482xx’s Address Table, the device
adds it to the table (indicating on which port the address resides). The GT-482xx then notifies the CPU (if present)
of the new address via a New_Address message.
3.2
Address Learning
The GT-482xx can learn up to 8K unique MAC addresses. Addresses are stored in the Address Table located in
the DRAM. The Address Table is managed automatically by the GT-482xx (i.e. a new address is automatically