78P7200L Просмотр технического описания (PDF) - TDK Corporation

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78P7200L

E3/DS3/STS-1 Transceiver

TDK Corporation 

FUNCTIONAL DESCRIPTION (continued)

LOSS OF SIGNAL

Should the input signal fall below a minimum value,

the loss of signal indication, LOS goes low.

TRANSMITTER

The transmitter accepts logic level clock (TCLK),

positive data (TPOS) and negative data (TNEG)

signals and generates current pulses on the LOUT+

and LOUT- pins. When properly connected to a

center-tapped 1:2 transformer, an AMI pulse is

generated which can drive a 75Ω coaxial cable.

When the recommended transformer is used and the

E# pin is set high, the transmitted pulse shape at the

end of the 75Ω terminated cable of 0 to 450 feet will

fit the DS3 template in ANSI T1.102-1993 and

Telcordia GR-499-CORE standard documents.

For STS-1 applications, the transmitted pulse for a

short cable meets the requirements of TelcordiaGR-

253-CORE. The E# pin should be allowed to float.

For E3 applications, the transmitted pulse for a short

cable meets the requirements of ITU-T G.703. The

E# pin is to be pulled low.

RCLK/TCLK POLARITY REVERSAL:

To simplify the interface with framer circuitry, RCLK

and TCLK can be inverted with the ICKP pin.

PIN 10

ICKP

Low

Float

High

RCLK

Normal

Invert

Normal

TCLK

Normal

Invert

Invert

78P7200L

E3/DS3/STS-1

Transceiver

LOOP-BACK MODES:

The following loop-back modes allow for the

diagnostic test of the PC board. This function is

controlled by the LPBK pin.

PIN 40/TQFP

PIN 28/PLCC

LPBK

Low

Float

High

LOOP-BACK

Local loop-back (LLB)

Remote loop-back (RLB)

Normal Operation

LOCAL LOOP-BACK:

When LPBK is low, the 78P7200L enters Local

loopback. In this mode, the LOUT+/- transmit signals

are internally routed to the receiver input circuit. The

incoming line receiver AMI signal on LIN+/- is

ignored. With the transmitter still tied to the cable,

this test mode can indicate a short circuit on the

transmitter external components or other problem in

the transmit path.

REMOTE LOOP-BACK:

When LPBK pin is allowed to float, the 78P7200L

enters remote loopback mode. The RPOS/RNEG

and RCLK pins are internally tied to the

TPOS/TNEG and TCLK so the same AMI signal that

is received by the framer is transmitted back to the

far end where a bit continuity test can be performed.

LINE BUILD-OUT:

The Line Build-Out function controls the amplitude in

DS3 and STS-1 mode. The selection of LBO

depends on the amount of cable the transmitter is

connected to. When used with less than 225 ft of

cable the LBO pin should be pulled high. With 225ft

or more cable the LBO pin should be low.

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