ACD82124 Datasheet, PDF (8/48 Pages) List of Unclassifed Manufacturers – 24 Ports 10/100 Fast Ethernet Switch Controller

This process is used to ensure that there are no
dropped frames. Backpressure flow control can be
disabled by setting the corresponding bit of the regis-
ter-21.
VLAN Support (register 23 & 24)
The ACD82124 can support up to 4 port-based secu-
rity VLANs. Each port of the ACD82124 can be as-
signed up to four VLAN. On power up, every port is
assigned to VLAN-0 as default VLAN. Frames from
the source port will only be forwarded to destination
ports within the same VLAN domain. A broadcast/
multicast frame will be forwarded to all ports within the
VLAN(s) of the source port. A unicast frame will be
forwarded to the destination port only if the destination
port is in the same VLAN as the source port. Other-
wise, the frame will be treated as a frame with un-
known DA. Each VLAN can be assigned with a dedi-
cated dumping port. Multiple VLANs can also share a
dumping port. Unicast frames with unknown destina-
tion addresses will be forwarded to the dumping port
of the source port VLAN.
Security VLAN can be disabled by setting the corre-
sponding bit in the system configuration register (bit 8
of Register 16). When security VLAN is disabled, each
VLAN becomes a leaky VLAN and is equivalent to a
broadcast domain. Four dumping ports of four differ-
ent virtual VLAN can be grouped together to form a fat
pipe uplink (For example, if port 0&1, port 2&3, port
3&4, port 5&6 are combined to form 4 full duplex ports
with 200Mbps per port throughput, these 4 full duplex
ports can be grouped to form an 800 Mbps uplink port).
When multiple dumping ports are grouped as a single
pipe, each port has to be assigned to one and only
one VLAN. A unicast frame with a matched DA will be
forwarded to any destination, even if the VLAN ID is
different. All unmatched DA packets will be forwarded
to the designated dumping port of the source port
VLAN. The broadcast and multicast packets will only
be forwarded to the ports in the same VLAN of the
source port. Therefore, a 200 to 800 Mbps pipe can
be established by carefully grouping the dumping ports,
and connects directly with the segmentation switches.
Dumping Port
Each VLAN can be assigned with a dedicated dump-
ing port. Multiple VLANs can share a dumping port.
Each dumping port can be used for up-link connec-
tion or for DTE connection. That is, the dumping port
can be used to connect the switch with a computer
repeater hub, a workgroup switch, a router, or any
type of interconnecting device compliant with the IEEE
802.3 standard. The ACD82124 will direct the follow-
ing frames to the dumping port:
• frame with unicast destination address that does
not match with any port’s source address within
the VLAN of the source port
• frame with broadcast/multicast destination address*
* See Spanning Tree Support
If the device is configured to work under Flood-to-All-
Port mode (Register 25, bit 8), frames listed above will
be forwarded to all the ports in the VLAN(s) of the
source port except the source port itself.
Mode of Operation
By default, all ports of the ACD82124 work in half du-
plex mode. A full-duplex port can be configured by
combining two half-duplex ports. In this case, the op-
eration mode of the port is determined by the port’s
PHY device through auto-negotiation. The mode of a
port can also be assigned by the duplex mode indica-
tion/assignment register (Register 27).
Spanning Tree Support
The ACD82124 supports Spanning Tree protocol.
When Spanning Tree Support is enabled (Register 16
bit 1), frames from the CPU port (port 23) having a DA
equal to the reserved Bridge Management Group Ad-
dress for BPDU will be forwarded to the port specified
by the CPU. Frames from all other ports with a DA
equal to the Reserved Group Address for BPDU will be
forwarded to the CPU port if the port is in the same
VLAN of the CPU port. Port 23 is designed as the
default CPU port. When Spanning Tree Support is dis-
abled, all reserved group addresses for Bridge Man-
agement is treated as broadcast address.
Every port of the ACD82124 can be set to block-and-
listen mode through the CPU interface. In this mode,
incoming frames with DA equal to the reserved Group
Address for BPDU will be forwarded to the CPU port.
Incoming frames with all other DA value will be dropped.
Outgoing frames with DA value equal to the Group Ad-
dress for BPDU will be forwarded to the attached PHY
device; all other outgoing frames will be filtered.
Queue Management
Each port of the ACD82124 has its own individual
transmission queue. All frames coming into the
ACD82124 are stored into the shared memory buffer,
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