HD-6409 Datasheet, PDF(6/12 Page) Intersil Corporation

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HD-6409 Datasheet, PDF (6/12 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. Manches-

ter 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 transi-

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

One is deï¬ned 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 5-10 octaves. It is much eas-

ier 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 pro-

duces 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

deï¬nes 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 num-

ber 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 tran-

sitions, 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 ï¬nal synchronization

advantage concerns the HD-6409âs sync pulse used to ini-

tiate synchronization. This three bit wide pattern is sufï¬-

ciently 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

LC Oscillator Mode

C1 = 32pF

16MHz

C0 = CRYSTAL + STRAY

X1 = AT CUT PARALLEL

RESONANCE

FUNDAMENTAL

MODE

RS (TYP) = 30â¦

OX R1 = 15Mâ¦

C1 = 20pF

C0 = 5pF

CE â C-----1-----â--2---2---C-----0--

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

2Ï LCe

FIGURE 5. CRYSTAL OSCILLATOR MODE

FIGURE 6. LC OSCILLATOR MODE

5-6

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