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CS61310

T1 Line Interface Unit

Cirrus Logic 

CS61310

2 THEORY OF OPERATION

The CS61310 Line Interface Unit is a fully inte-

grated transceiver for T1 long haul applications.

The transmitter outputs all pulse shapes for T1 ap-

plications.

2.1 Interface Modes

The CS61310 can be operated as a stand-alone de-

vice with its interface in hardware mode (MODE

pin is low), or it can be operated by a microcontrol-

ler over a serial interface in host mode (MODE pin

is high). Host mode enables the use of additional

functionality, as described in the Serial Interface

section.

2.2 Master Clocks

The CS61310 requires a reference clock for the re-

ceiver and the jitter attenuator. A 1.544 MHz exter-

nal clock can be input to MCLK, or a 4x crystal can

be connected to the on-chip oscillator. This fre-

quency reference should be within +32 ppm of the

nominal operating frequency. Jitter and wander on

the reference clock will degrade jitter attenuation

and receiver jitter tolerance. If MCLK is provided,

the crystal oscillator is ignored.

2.3 Transmitter

The transmitter accepts digital T1 input data and

drives appropriately shaped AMI (Alternate Mark

Inversion) pulses onto a transmission line through

a transformer. The transmit data (TPOS & TNEG

or TDATA) is sampled on the falling edge of the

input clock, TCLK.

The pulse shapes comply with FCC Part 68 Option

A (0 dB), Option B (-7.5 dB), Option C (-15 dB) or

(-22.5 dB) (see Table 1). Pulse shaping and signal

level are controlled by LBO1 and LBO2 pins in

hardware mode, or the LBO1 and LBO2 bits

(CR1.3 and CR1.4) in host mode.

Custom transmit pulse shapes may be implemented

by writing pulse shape coefficients to the registers.

LB02

0

0

1

1

LB01

0

1

0

1

Output Pulse

0 dB

-7.5 dB

-15 dB

-22.5 dB

Table 1. Pulse Shape Selection and Transformer

Requirements

Custom pulses may be used to correct for pulse

shape degradation or distortion caused by improper

termination, suboptimal interconnect wiring, or

loading from external components such as high

voltage protection devices.

For DS-1 applications, the arrangement in Table 1

meets ANSI T1.102 pulse shape requirements. A

typical output pulse is shown in Figure 6. These

pulse settings can also be used to meet ITU-T pulse

shape requirements for 1.544 MHz operation.

NORMALIZED

AMPLITUDE

1.0

0.5

ANSI TI.102

SPECIFICATION

0

-0.5

0

OUTPUT

PULSE SHAPE

250

500

750

TIME (nanoseconds)

1000

Figure 6. Typical Pulse Shape for DS-1

8

DS440PP2

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