HD6409_15 Datasheet, PDF(6/15 Page) Intersil Corporation

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HD6409_15 Datasheet, PDF (6/15 Pages) Intersil Corporation – CMOS Manchester Encoder-Decoder

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HD-6409

Manchester Code

Nonreturn-to-Zero (NRZ) code represents the binary values

logic-O and Iogic-1 with a static level maintained throughout

the data cell. In contrast, Manchester code represents data

with a level transition in the middle of the data cell.

Manchester has bandwidth, error detection, and

synchronization advantages over NRZ code.

The Manchester II code Bipolar One and Bipolar Zero shown

below are logical complements. The direction of the

transition indicates the binary value of data. A logic-0 in

Bipolar One is defined as a Low to high transition in the

middle of the data cell, and a logic-1 as a high to low mid bit

transition, Manchester Il is also known as Biphase-L code.

The bandwidth of NRZ is from DC to the clock frequency fc/2,

while that of Manchester is from fc/2 to fc. Thus, Manchester

can be AC or transformer coupled, which has considerable

advantages over DC coupling. Also, the ratio of maximum to

minimum frequency of Manchester extends one octave, while

the ratio for NRZ is the range of 5 to 10 octaves. It is much

easier to design a narrow band than a wideband amp.

Secondly, the mid bit transition in each data cell provides the

code with an effective error detection scheme. If noise

produces a logic inversion in the data cell such that there is

no transition, an error indiction is given, and synchronization

must be re-established. This places relatively stringent

requirements on the incoming data.

The synchronization advantages of using the HD-6409 and

Manchester code are several fold. One is that Manchester is

a self clocking code. The clock in serial data communication

defines the position of each data cell. Non self clocking

codes, as NRZ, often require an extra clock wire or clock

track (in magnetic recording). Further, there can be a phase

variation between the clock and data track. Crosstalk

between the two may be a problem. In Manchester, the

serial data stream contains both the clock and the data, with

the position of the mid bit transition representing the clock,

and the direction of the transition representing data. There is

no phase variation between the clock and the data.

A second synchronization advantage is a result of the

number of transitions in the data. The decoder

resynchronizes on each transition, or at least once every

data cell. In contrast, receivers using NRZ, which does not

necessarily have transitions, must resynchronize on frame

bit transitions, which occur far less often, usually on a

character basis. This more frequent resynchronization

eliminates the cumulative effect of errors over successive

data cells. A final synchronization advantage concerns the

HD-6409âs sync pulse used to initiate synchronization. This

three bit wide pattern is sufficiently distinct from Manchester

data that a false start by the receiver is unlikely.

BIT PERIOD

BINARY CODE

NONRETURN

TO ZERO

BIPOLAR ONE

BIPOLAR ZERO

FIGURE 4. MANCHESTER CODE

Crystal Oscillator Mode

16MHz

C1 = 32pF

C0 = CRYSTAL + STRAY

X1 = AT CUT PARALLEL

RESONANCE

FUNDAMENTAL

MODE

RS (TYP) = 30ï

OX R1 = 15Mï

LC Oscillator Mode

C1 = 20pF

C0 = 5pF

CE ï» C-----1-----â--2---2---C-----0--

ï»

-----------1------------

2ï° LCe

FIGURE 5. CRYSTAL OSCILLATOR MODE

FIGURE 6. LC OSCILLATOR MODE

FN2951.4

October 1, 2015

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