MTD508 Myson Technology, MTD508 Datasheet - Page 9

• Manufacturer Part Number: MTD508
• Description: 8-port Switch
• Manufacturer: Myson Technology

Myson-Century Technology
MTD508
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FUNCTIONAL DESCRIPTION
The MTD508 is an 8-port 10/100Mbps fast Ethernet switch controller. It is a low-cost solution for eight ports fast
Ethernet SOHO switch design. No CPU interface is required. After power on reset, the MTD508 provides an auto
load configuration setting function through a 2-wire serial EEPROM interface to access external EEPROM
device, and the MTD508 can easily be configured to support port-trunking, port-VLAN, static entry, 802.3x flow
control threshold setting, flooding port assignment... etc. functions. The following descriptions are the MTD508’s
major function blocks overview.
Packet Store and Fowarding
The MTD508 uses simple store and forward algorithm as packet switching method. Input packet from ports will
be stored to external memory first, while packet is good for forwarding (CRC check okay, 64Bytes < length <
1518Bytes, not local packets, in the same VLAN group), if this packet’s DA hits, then forward this packet to the
destination port, otherwise this packet will be broadcasted.
Learing and Routing
The MTD508 supports 1K or 8K MAC entries for switching. Dynamic address learing is performed by each good
unicast packet is completely received. The static address learning achieved by EEPROM configuration. On the
other hand, the routing process is performed whenever the packet’s DA is captured. If the DA cannot get a hit
result, the packet is going to switch broadcast or forward to the dedicated port according to the flooding control
selection.
Aging
Only the dynamic address entries are scheduled int he aging machine. If one station does not transmit any
packet for a period of time, the belonging MAC address will be kicked out from the address table. The aging out
time can be programmed through the EEPROM auto load configuration. (Default value is 300 seconds.)
Buffer Queue Management
The buffer queue manager is implemented to manage the external shared memory (use SDRAM/SGRAM) for
packet buffering. The main function of the buffer queue manager is to maintain the linked list sonsisted of buffer
IDs, which are used to show the corresponding memory address for each incoming packet. in addition, the buffer
queue manager monitors the rested free spaces status of the external memory. If the packet storage achieves
the predefined threshold value, the buffer queue manager will raise the alarm signal which is used to enable the
flow control mechanism for avoiding transmission ID queue overflow happening. The MTD508 provides 802.3x
flow control in full duplex mode and back pressure control in half duplex mode.
Full Duplex 802.3x Flow Control
In full duplex mode, the MTD508 supports the standard flow control defined in IEEE802.3x standard. It enables
the stopping of remote node transmissions via a PAUSE frame information interaction. When the “802.3x flow
control enable” bit is set during power on reset (LEDDATA[7] pin is external pull_high), it enables the MTD508
supporting 802.3x flow control function in full duplex mode; when output port buffer queue’s on-using value
reaches the initialization setting threshold value (recommended Xon_TH = 74h when using 2Mbytes external
memory; Xon_TH = 2eh when using 1Mbytes external memory), the MTD508 will send out a PAUSE packet with
pause time equal to FFF to stop the remote node transmission. When the output port buffer queue’s on-using
value reduces to the initialization threshold value (recommended Xoff_TH = 30h when using 2Mbytes external
memory; Xoff_TH = 18h when using 1Mbytes external memory), the MTD508 will also send a PAUSE packet with
pause time equal to zero to inform the remote node to retransmit packet.
Half Duplex Back Pressure Control
In halp duplex mode, the MTD508 provides a back pressure control mechanism to avoid dropping packets during
network congestion. When the “back pressure control enable” bit is set during power on reset (LEDDATA[6]pin is
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