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參數(shù)資料
| 型號(hào)： | LXT917QC |
| 英文描述： | LAN Transceiver |
| 中文描述： | 網(wǎng)絡(luò)收發(fā)器 |
| 文件頁數(shù)： | 15/42頁 |
| 文件大?。?/td> | 561K |
| 代理商： | LXT917QC |
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Flexible Quad Ethernet Repeater
—
LXT914
Datasheet
15
2.2.3
Serial Port
The serial port provides the management interface to the LXT914. Refer to Test Specifications for
serial port timing. The serial port can be either unidirectional or bidirectional, depending on the
management mode selected. In the Local management mode the serial port is unidirectional (input
only), and is used only to download setup parameters during initialization. The Local mode is
intended for use with a simple EEPROM, but the serial port may be tied Low if an EEPROM is not
required.
In the External management mode, the serial port is bi-directional (input for setup parameters,
output for status reports). The External mode is intended for use with an External Management
Device (EMD) and a Media Access Controller (MAC). The EMD (typically a gate array)
communicates with a microprocessor (e.g., Intel 8051) and can control up to three LXT914
repeaters. This simplifies design of a relatively standard 12-port repeater on a single printed circuit
board.
2.2.4
Inter-Repeater Backplane
The Inter-Repeater Backplane (IRB) allows several LXT914s to function as a single repeater. Refer
to Test Specifications for IRB timing. The IRB also allows several multi-repeater boards to be
integrated in a standard rack and to function as a single unit. The IRB supports
“
hot swapping
”
for
easy maintenance and troubleshooting. Each individual repeater distributes recovered and re-timed
data to other repeaters on the IRB for broadcast on all ports simultaneously. This simultaneous
rebroadcast allows the multi-repeater system to act as a single large repeater unit. The maximum
number of repeaters on the IRB is limited by bus loading factors such as parasitic capacitance. The
IRB can be operated synchronously or asynchronously.
2.2.4.1
Synchronous IRB Operation
In the synchronous mode, a common external source provides the 10 MHz backplane clock
(BCLKIO) and the 20 MHz system clock (SYSCLK) to all repeaters. BCLKIO must be
synchronous to SYSCLK and may be derived from SYSCLK using a divide-by-two circuit. In the
synchronous mode 32 or more LXT914 repeaters may be connected on the IRB, providing 128
10BASE-T ports and 32 AUI ports.
2.2.4.2
Asynchronous IRB Operation
In the asynchronous mode an external BCLKIO source is not required. The repeaters run
independently until one takes control of the IRB. The transmitting repeater then outputs its own 10
MHz clock onto the BCLKIO line. All other repeaters sync to that clock for the duration of the
transmission. In the asynchronous mode 12 or more LXT914 devices may be connected to the IRB,
providing 48 10BASE-T ports and 12 AUI ports.
Note:
The maximum number of repeaters which may be linked on the backplane is limited by board
design factors. The numbers listed above are engineering estimates only. Stronger drivers and
reduced capacitive loading in PCB layout may allow an increased device count.
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