STLC1502 datasheet(21/81 Pages) STMICROELECTRONICS

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STLC1502

tion from the ARM controller.

•

In receive, when the complete frame is stored in memory, the DMAC asserts the interrupt for the

ARM that can read the frame.

•

In transmit the DMAC provides an interrupt when the complete frame is transferred.

6.5 Ethernet Switch

The Ethernet switch block interfaces two MAC cores to implement a 3-port Ethernet Fast switch and MAC layer

for the Embedded VoIP network software.

Main features of the block are:

•

Internal FIFOs for easy DMA transfers.

•

Full duplex support using separate Tx, Rx FIFOs.

•

Fast switching using hardware connections between the two MAC cores. ARM microcontroller is not

involved in the switching function.

•

Support for priority mechanism for voice packets, using store-and-forward procedure for incoming

data packets.

•

VLAN support

•

10/100 Mb/s data transfer rates

•

The MAC cores provide 2 MII interfaces to connect two external PHYs.

The device works normally as a bidirectional switch between the two ports. When the following conditions hap-

pen the device triggers additional operations:

•

Received frame destination MAC address matches device MAC address. The frame is transferred to

memory using DMA, and is not switched to the other port.

•

A frame has to be transmitted by the device. In this case the block waits for the end of the current

frame being switched if any. If the frame is a voice frame, as soon as the line is free the block starts

transfer of the frame. Eventual incoming frames in the same direction are stored and forwarded after

the voice frame has been sent.

The block diagram of the Ethernet switch is shown below:

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