78P2253-IGT Просмотр технического описания (PDF) - TDK Corporation

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78P2253-IGT

E4/STM-1/STS-3/OC-3 Transceiver

TDK Corporation 

TRANSMITTER OPERATION (continued)

XTAL1

XTAL2

CKIN

FIGURE 1A: USING CRYSTAL

XTAL1

XTAL2

CKIN

17.283 MHz (E4)

19.440 MHz (Sonet)

FIGURE 1B: USING EXTERNAL CLOCK

In ECL mode the data signal is converted to CMI

code by the Binary to CMI encoded.

The HUB/HOST input changes the reference signal

for the clock generator. In the hub mode (HUB/HOST

high), the transmit clock reference is derived from

either the crystal oscillator or CKIN. In host mode

(HUB/HOST low), the transmit clock reference is

derived from the recovered receive clock.

78P2253

E4/STM-1/STS-3/OC-3

Transceiver

RECEIVER OPERATION

The receiver accepts serial, CMI coded data, at

155.52Mbit/s or 139.264Mbit/s from either the CMI

or the ECL inputs. In CMI mode, the inputs CMIINP

and CMIINN receive the input signal from a coaxial

cable that is transformer-coupled to the chip. The

ECL pins should be left open. In ECL mode, the pins

ECLINP and ECLINN receive the input signal.

In CMI mode, the received signal is equalized for

dispersive cable attenuation and decoded in the CMI

to binary decoder.

A clock signal is recovered using a low jitter PLL

circuit.

The data is converted to binary by the CMI to Binary

decoder.

In serial mode, the received data is output on the

RXDTP and RXDTN pins and the recovered clock is

output on the RXCKP and RXCKN pins.

In parallel mode, the received data is converted to

parallel, eight bits if 8BIT/$BIT is high and four if it is

low. The first bit received will arrive on the most

significant output pin, RXDT[7] in eight bit mode and

RXDT3 in four bit mode.

The LOS pin goes high when the signal detector

detects a loss-of-signal condition.

LOOPBACK OPERATION

The 78P2253 is capable of performing signal

loopback in two ways The RLBACK pin selects the

remote loopback mode. In this mode, the received

signal is “looped back” and sent out of transmitter in

place of the transmit input signal.

The LLBACK pin selects the local loop-back mode,

and causes the receiver to use the transmitter output

signal as its input. Local loopback is disabled when

HUB/HOST is low or RLBACK is high.

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