MTD505 Datasheet, PDF (10/19 Pages) List of Unclassifed Manufacturers – 5 Port 10M/100M Ethernet Switch

MYSON
TECHNOLOGY
MTD505
(Preliminary)
3.6 Half Duplex Back Pressure Control
In half duplex mode, MTD505 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 (LEDDATA[6] pin is external pull_high), it enables MTD505 supporting back pressure function in
half_duplex mode; When output port buffer queue’s on_using value reach the initialization setting
threshold value (same with the Xon_TH value), MTD505 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 dropping packets. If the “back pressure control enable” bit is not set, and
there is no free buffer queue available for the incoming packets, the incoming packets will be dropped.
3.7 MII Polling
The MTD505 supports PHY management through the serial MDIO/MDC interface. After power on
reset, the MTD505 write related abilities to the advertisement register 4 of connected PHY devices and
restart the auto_negotiation prcedure via MDIO/MDC interface using the predefined PHY addresses
increasingly from “01000”b to “01100”b. The MTD505 will periodically and continuously poll and update
the link status and link partner’s ability which include speed, duplex mode, and 802.3x flow control
capable status of the connected PHY devices through MDIO/MDC serial interface.
3.8 MAC and DMA engine
The MTD505’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, alignment
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 (MTD505 implements the truncated exponential back_off algorithm defined in IEEE
802.3 standard). For the full duplex mode, collision signal is ignored.
The MTD505’s DMA engine performs the packets non_blocking transportation between MAC engine
and external memory according to a high speed switching procedure. The switching procedure is com-
pleted by address learning/routing process and buffer queue management operation.
3.9 EEPROM interface
MTD505 provide an auto load configuration setting function through a 2 wire serial EEPROM interface
to acess external EEPROM device(24C02) after power on reset . MTD505 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 table is the EEPROM contents mapping:
Name
EOB
AgeLow
AgeHigh
VLAN0
VLAN1
VLAN2
VLAN3
VLAN4
EEPROM
Address
00
01
02
03
04
05
06
07
EEPROM Content Description
Last EEPROM content address value
Aging Time bit [7:0]
Aging Time bit [15:8]
Port0 VLAN register
Port1 VLAN register
Port2 VLAN register
Port3 VLAN register
Port4 VLAN register
Recommended
Value Under
Basic Operation
8’h13
8’h2c
8’h01
8’hfe
8’hfd
8’hfb
8’hf7
8’hef
10/19
MTD505 Revision 1.2 14/04/2000