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參數(shù)資料
| 型號： | GT-48004A |
| 廠商： | Galileo Technology Services, LLC |
| 英文描述： | Four Port Switched Fast Ethernet Controller(四端口、交換式快速以太網(wǎng)控制器) |
| 中文描述： | 四端口交換式快速以太網(wǎng)控制器（四端口，交換式快速以太網(wǎng)控制器） |
| 文件頁數(shù)： | 58/106頁 |
| 文件大?。?/td> | 953K |
| 代理商： | GT-48004A |
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GT-48004A Four Port Switched Fast Ethernet Controller
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Revision 1.0
N:\Marketing\Docs\Archive\48004A\DATASHEET\Rev 1.0\484ads10.fm
13.9
10/100 Mbps Full-Duplex Operation
When operating in Full-duplex mode the GT-48004A can transmit and receive frames simultaneously. In full-duplex
mode, the CrS signal is associated with received frames only and has no effect on transmitted frames. The Col signal
is ignored by the GT-48004A while in Full-duplex mode. Transmission starts when TxEn goes active. Transmission
starts regardless of the state of RxDV. Reception starts when the RxDV signal is asserted indicating traffic on the
receive port of the PHY.
13.10 Illegal Frames
The GT-48004A will discard all illegal frames and increment the appropriate error MIB counters. Examples include:
runts (less than 64 bytes), oversize (greater than 1518 or 1522 bytes), and bad FCS (bad CRC.)
13.11 Partition Mode
A port enters Partition Mode when more than 61 consecutive collisions are seen on the port (whether the port is run-
ning at 10 or 100 Mbps). In Partition Mode the port continues to transmit but it will not receive. The PaEn bit in the cor-
responding Port Control register is set when a port is partitioned. A port is returned to normal operation mode when a
good packet is seen on the wire.
13.11.1 Enabling Partition Mode
Partition is enabled (for all ports) by setting the enable bit in the GT-48004A Control Register. The default value is Par-
tition disabled for all ports. You must have a CPU in the system to enable partition mode, there is no pin strapping
option.
13.11.2 Entering Partition State
When Partition is enabled, a port will enter Partition state when either of the following two situations occur:
The port detects a collision on every one of 61 consecutive retransmit attempts of the same packet.
The port detects a single collision which occurs for more than 512 bit times
While in Partition state:
If the interrupt is not masked, the GT-48004A will issue an interrupt to the CPU upon entering Partition state,
and will set the partition bit of that port in the Interrupt Cause register.
The port will continue to transmit its pending packet, regardless of the collision detection, and will not follow the
usual Backoff Algorithm. Additional packets pending for transmission, will be transmitted, while ignoring the
internal collision indication. This frees the port's transmit buffers which would otherwise be filled up at the
expense of the other ports' buffers. The assumption is that Partition is a system failure situation (bad connec-
tor/cable/station), thus dropping packets is a small price to pay vs. the cost of halting the switch due to full buff-
ers.
The Partition Indication is available via the LED interface (both the status led - blinking twice, and a dedicated
led - on constantly).
13.11.3 Exiting from Partition State
The port will exit from Partition state, following the end of a successful packet transmission or packet reception. A suc-
cessful packet transmission will be declared, if no collisions were detected during packet transmit or receive. If the
interrupt is not masked, the GT-48004A will issue an interrupt to the CPU upon exiting from Partition state, and will
clear the partition bit of that port in the Interrupt Cause register.
13.12 Back-pressure
Back-pressure is not supported by the GT-48004A. Back-pressure can greatly deteriorate real network throughput in
favor of better standardized test scores. Back-pressure works is by “jamming” an entire network segment when the
switch cannot accept new transmissions. This blocks
all traffic, including traffic between nodes on the same network
segment (like blocking local phone calls when the long distance circuits are busy.) Simply dropping packets is a better
solution for overall network throughput, although this is not reflected in some simplistic standardized tests. (Dropped
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