MTD502E ETC-unknow, MTD502E Datasheet - Page 16

• Manufacturer Part Number: MTD502E
• Description: 2 Port 10m/100m Switch With Build_in Memory
• Manufacturer: ETC-unknow

4.0 FUNCTIONAL DESCRIPTIONS
The MTD502E implements a 10/100M two port switch for 10M/100M packet switching. Total 2K
address entrys are provided for packets’ SA learning and DA routing; and also provide automatic aging
function ( aging time = 300secs). When using in two port bridge application, the input packets from
port0 will be stored in an embedded memory buffers of MTD502E first, while packets is good for for-
warding ( CRC chech ok, 64Bytes < length > 1518Bytes, and not local packets ) , than forward this
packet to port1.
4.1 Learning and Routing
The MTD502E supports 2K MAC entries for filtering. Dynamic address learning is performed by each
good unicast packet is completely received. The routing process is performed whenever the packet’s
DA is captured. If the DA get a hit result in self port ’ s address table, this packet will be treated as a “
local packet”, and then drop the packet forwarding to the other port. On the other hand, if this packet is
not a “local packet”, then will be forwarded to the other port.
4.2 Aging
The address entries are scheduled in the 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 value is 300 seconds.
4.3 Buffer Queue Management
The buffer queue manager is implemented to manage the embedded memory packet buffering. The
main function of the buffer queue manager is to maintain the linked list consists of buffer IDs, which is
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 memory buffers, If the packet storage
achieve 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.
MTD502E provide back pressure control scheme in half duplex mode.
4.4 Half Duplex Back Pressure Control
In half duplex mode, MTD502E provide a back pressure control mechanism to avoid dropping packets
during network conjection situation. When the “back pressure control enable” bit is set during power on
reset (pin_18 is external pull_low), it enables MTD502E supporting back pressure function in
half_duplex mode; When output port buffer queue’ s on_using value reach the initialization setting
threshold value, MTD502E will send a JAM pattern in the input port when it senses an incoming packet
, thus force a collision to inform the remote node transmission back off and will effectively avoid drop-
ping packets. If the “back pressure control disable” bit is set, and there is no free buffer queue available
for the incoming packets, the incoming packets will be dropped.
4.5 MAC and DMA engine
The MTD502E’s MAC performs all the functions in IEEE802.3 protocol, such as frame formatting,
frame stripping, CRC checking, bad packet dropping, defering to line traffic, and collision handling. The
MAC Rx_engine checks incoming packets and drops the bad packet which include CRC error, align-
ment error, short packet (less than 64 bytes), and long packet(more than 1518 bytes or 1522 bytes
when the “VLAN tag 1522 bytes receive enable” bit is set during power on reset). Before transmission,
The MAC Tx_engine will constantly monitor the line traffic using derfering precedure. Only if it has been
idle for a 96 bits time (a minimum interpacket gap time, IPG time), actual transmmission can be started.
For the half duplex mode, MAc engine will detect collision; if a collision is detected, the MAC Tx_engine
will transmit a JAM pattern and then delay the re_transmission for a random time period determined by
the back_off algorithm (MTD502E implements the truncated exponential back_off algorithm defined in
IEEE 802.3 standard). For the full duplex mode, collision signal is ignored.
MYSON
TECHNOLOGY
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MTD502E Revision 1.3 12/07/2000
MTD502E