ACD81024 データシートの表示（PDF） - Unspecified

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ACD81024

24 Ports Single Chip 10Base-T Ethernet Switch Designed For Desktop Environment

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1 frame with unicast destination address and

update the value of the MAC address storage of the

does not match with any port MAC address of source port. The value of DA is used to identify the

the switch

destination port.

2 frame with broadcast/multicast address

3 frame dumped to keep DTE address alive (see

section of “Address Keep Alive Handling”)

4.4 Switch Fabric Module

Address Keep Alive Handling

The address learned by an interconnection device

has a limited life cycle. To keep the address of the

DTEs connected with the switch alive in the intercon-

nection device connected with the expansion port of

the switch, ACD81024 can be set to dump at least

one frame to the expansion port for every five min-

utes. This function can be disabled by pulling low of

the DMPE signal.

Half Duplex Operation Mode

ACD81024 can only work in half duplex mode. Any

concurrent transmit and receive activities will be

treated as collision.

Spanning Tree Handling

Switch Fabric is responsible for establishing the

connection channel(s) from a source port to the

corresponding destination port(s). ACD81024 imple-

ments a cross-bar type switch fabric that allows high

efficient multiple channels of simultaneous connec-

tions.

4.5 Fabric Control Module

Fabric Control Logic controls the process of construc-

tion/destruction of the communication channel in the

Switch Fabric. Before a connection can be made,

Fabric Control logic first checks the status of the

destination port(s), to see if it is suitable to open the

path. Fabric Control logic is responsible to notify the

source MAC logic if the requested connection has

been made or not.

Only port 24 of ACD81024 can be used to connect

with an interconnection device which support multiple

MAC addresses. All other ports of ACD81024 should

only be used to connect with one desktop DTE with

only one MAC address. Therefore, it is not necessary

to handle Spanning Tree protocol to avoid formation

of a loop.

Latency

The latency, defined by the time difference between

the first bit enters into ACD81024 and first bit comes

out of ACD81024, is a constant value of 146 Bit Time.

Collision Domain

Different from typical Ethernet switch, ACD81024

does not isolate the collision domain between the

source DTE and the destination DTE. Therefore, the

latency of ACD81024 needs to be counted as part of

the delay path. The delay on the forward path is 146

Bit Times. The delay on the backward path (for

collision detection) is 4 Bit Times.

4.3 Lookup Engine Module

The lookup engine is responsible to provide mapping

between a MAC address and a port number. It

contains one MAC address storage for each port. The

value of SA embedded inside the frame is used to

4.6 LED Control Module

Just like a shared media repeater system, ACD81024

is designed to have a wide variety of LED indicators

for simple system administration. The display update

is completely autonomous and merely requires low

speed TTL or CMOS devices as LED drivers. The

status display is designed to be flexible to allow the

system designer to choose those indicators appropri-

ate for the specification of the equipment.

There are two LED control signals. LEDVLD signal is

used to indicate the start and end of the LED data

signal. LEDCLK signal is a 1MHz clock signal. The

rising edge of LEDCLK can be used to latch the LED

data signal into the LED driver circuitry.

The LED data signals contain Lnk, Xmt, Rcv, Col,

Fbe, Jbr, Addr and Bsy, which represent Link status,

Transmit status, Receive status, Collision indication,

Frame Bit Error, Jabber error, Port Address Learned

status, and Congestion Control status respectively.

These status signals are sent out sequentially from

port one to port twenty-four, once every 100ms. For

details about the timing diagrams of the LED signals,

refer to the chapter of “Signal Waveforms.”

5. SPECIAL HANDLING ON 802.3

ACD Confidential. Do Not Reproduce. Use under Non-Disclosure agreement only.

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