RTL8305SB-VD
Datasheet
1. General Description
The RTL8305SB-VD is a 5-port Fast Ethernet switch controller that integrates memory, five MACs, and
five physical layer transceivers for 10Base-T and 100Base-TX operation into a single chip. All ports
support 100Base-FX, which shares pins (TX+-/RX+-) with UTP ports and needs no SD+/- pins, a
development using Realtek proprietary technology. To compensate for the lack of auto-negotiation in
100Base-FX applications, the RTL8305SB-VD can be forced into 100Base-FX half or full duplex mode,
and can enable or disable flow control in fiber mode.
The five ports are separated into three groups (GroupX/GroupY/Port4) for flexible port configuration
using strapping pins upon reset. The SetGroup pin is used to select port members in GroupX and GroupY.
When the port members have been determined, you may use a mode selection pin
(GxMode/Gymode/P4Mode[1:0]) to select operating interfaces such as 10/100Base-TX, 100Base-FX.
Each group has 4 pins for selecting initial port status (ANEG/Force, 100/10, Full/Half, Enable/Disable
Flow Control) upon reset. Upon reset, in addition to using strapping pins, the RTL8305SB-VD can also
be configured via an EEPROM or read/write operation by a CPU through the MDC/MDIO interface.
The fifth port (port 4) supports an external MAC and an external PHY interface. The external MAC
interface can be set to PHY mode MII, PHY mode SNI, or MAC mode MII to work with a routing
engine, HomePNA, or VDSL transceiver. The external PHY interface can be set to PHY mode MII in the
digital interface, and UTP or fiber in the differential interface. In order to accomplish diagnostics in
complex network systems, the RTL8305SB-VD also provides a loopback feature in each port for a
variable CPU system.
The RTL8305SB-VD contains a 1K entry address look-up table and supports a 16-entry CAM to avoid
hash collisions and to maintain forwarding performance. The RTL8305SB-VD supports IEEE 802.3x full
duplex flow control and back-pressure half duplex flow control. A broadcast storm filtering function is
provided to filter unusual broadcast storm issues and an intelligent switch engine prevents Head-Of -Line
blocking problems.
The RTL8305SB-VD supports five VLAN groups. These can be configured as port-based VLANs and/or
802.1Q tag-based VLANs. Two ingress filtering and egress filtering options provide flexible VLAN
configuration:
• Ingress filtering option 1: The Acceptable Frame Type of the Ingress Process can be set to ‘Admit
All’ or ‘Admit All Tagged’
• Ingress filtering option 2: Frames associated with a VLAN for which that port is not in the
member set can be ‘Admit’ or ‘Discard’
• Egress filtering option 1: ‘Forward’ or ‘Discard’ARP broadcast frames
• Egress filtering option 2: ‘Forward’ or ‘Discard’ Leaky VLAN frames
The RTL8305SB-VD supports several types of QoS functions with two-level priority queues to improve
multi-media or real-time networking applications. The QoS functions are based on:
• Port-based priority
• 802.1Q VLAN priority tag
• The TOS/DS (DiffServ) field of TCP/IP
In order to avoid the flow control function effecting the quality of high priority frames, the
RTL8305SB-VD supports intelligent flow control for high priority frames by setting DisFCAutoOff to
automatically turn off flow control for 1~2 seconds whenever a congested port receives high priority
frames. When the QoS function is enabled, a VLAN tag can be inserted or removed at the output port.
The RTL8305SB-VD will insert a VLAN priority-tag (VID=0x000) for untagged frames or remove the
5-port 10/100Mbps Single-Chip Dual MII Switch Controller
1
Track ID: JATR-1076-21 Rev. 1.5
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