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ACS4110

Acapella Optical Modem IC

Semtech Corporation 

System Frequencies and Clock Generation

The crystal clock frequency and the multiplying factors

of the MPLL are determined by the choice of data

rates. Table 2 lists the required frequencies of the

system.

It is anticipated that most users of the ACS411CS

will interface directly with a E1/T1 framers. All the

popular framers provide POS/NEG bipolar interfaces

which will directly connect to the ACS4110.

If required, a detailed description of the AMI/HDB3/

BxZS coding rules are available from Acapella.

Mode

Data Rate XTAL

MHz

MHz

Fsys

MHz

16 x T1

16 x E1

7 x T2

4 x E2

1 x E3

1 x T3

1 x OC1

1.544

2.048

6.312

8.448

34.368

44.736

51.840

23.160

22.528

23.144

22.528

22.912

22.368

25.920

69.480

67.584

69.432

67.584

68.736

67.104

77.760

Table 2: System frequencies

Data Coding

The main synchronous channels may use any of the

following coding methods: NRZ, AMI, HDB3, B3ZS,

B6ZS and B8ZS. The desired mode is selected by

POL(3:1) input pins, as shown in Table 3.

Data

Coding

POL3

POL2

POL1

NRZ

AMI

HDB3

B8ZS

B6ZS

B3ZS

NRZ

NRZ

0

0

0

0

0

1

0

1

0

0

1

1

1

0

0

1

0

1

1

1

0

1

1

1

Table 3: Line coding selection

For Non-Return-to-Zero (NRZ) coding, data is applied

directly to TPOS inputs, and output data appears

only on the RPOS output pins. When using NRZ

code, unconnected TNEG input pins will automatically

pull-up to VD+. In addition, the ACS411CS will assert

a continuous Low on redundant RNEG output pins.

AMI, B3ZS, B6ZS, B8ZS and HDB3 coding is

normally bipolar. However, it is possible to interface

with the ACS411CS using two inputs and outputs

rather than a single bipolar interface. Data equivalent

to positive excursions of the bipolar AMI/BxZS/HDB3

signal are applied as a logic High to TPOS, while

data equivalent to negative excursions are applied

as a logic High to TNEG. Similarly, AMI/BxZS/HDB3

positive excursions will appear as a logic High on

RPOS and negative excursions will appear as a logic

High on RNEG.

Data Rate Selection

For the purpose of this specification TPN1 represents

the set of signals TPOS1 and TNEG1, and RPN1

represents the set of signals RPOS1 and RNEG1.

See section headed, Data Coding for a description

of the coding types.

The maximum recommended crystal (XTAL) is

26.88MHz. An internal multiplier factors the XTAL

frequency by 3. The maximum bandwidth is

51.840MHz (OC1). This bandwidth can be utilised

in various ways, it may be divided up over 1, 4, 7 or

16 channels.

All 16 main channels are completely independent. One

channel consists of the following 6 signals:

Transmit side:

TPOS

+ve in bipolar signal or NRZ data

TNEG

-ve in bipolar signal TPOS

TCLK

transmit clock (internal or external)

Receive side:

RPOS

+ve in bipolar signal or NRZ data

RNEG

-ve in bipolar signal or NRZ data

RCLK

receive clock

The data rate can be selected via the data rate selection

bits DR(4:1), either directly via pins or via the

microprocessor interface. The selection determines

the number of active channels in combination with the

selected crystal frequency and the line data rate in

accordance with Table 4.

DR Pins

32 1

TCLK

(MHz)

Nos. of Tmode

channels

1 10

1 01

1 00

0 11

0 10

0 01

0 00

1.544

16

2.048

16

6.312

7

8.448

4

34.368

1

44.736

1

51.840

1

16 x T1

16 x E1

7 x T2

4 x E2

1 x E3

1 x T3

1 x OC1

Table 4: Data rate and channel selection

Channels not used in a specific mode are disabled. For

example in 4 x E2 mode channels 1 to 4 are carrying

E2 data rates, and channels 5 to 16 are disabled. All

channels can be disabled individually via the

microprocessor interface, or alternatively via far-end

remote control.

7

ACS411CS PRE-RELEASE Issue 6.0 July 1999.

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