MC33593

MOTOROLA SEMICONDUCTORS PRODUCTS

5

revision 7.0, 5 February 2002

© Motorola, Inc., 2002.

COMMUNICATION PROTOCOL

MANCHESTER CODING DESCRIPTION

Manchester coding is defined as follows: data is sent during the first half-bit, complementary data is sent

during the second half-bit.

Figure 3: Manchester coding example

The signal average value is constant. This allows clock recovery from the data stream itself. In order to

achieve a correct clock recovery, Manchester coded data must have a duty cycle between:

- 48% and 52% in OOK,

- 45% and 55% in FSK.

PREAMBLE, ID, HEADER WORDS AND MESSAGE DESCRIPTION

The following description applies if the Data Manager is enabled (DME=1).

The ID word is a Manchester coded byte whose content has been previously loaded in the Configuration

Register 2. The complement of the ID word is recognized as an ID word. ID word is sent at the same data rate as

data.

A preamble is required:

- before ID,

- before Header if HE=1,

- before data if HE=0.

It enables:

- in case of OOK modulation, AGC to settle,

- in case of FSK modulation, data slicer reference voltage to settle,

- in any case, clock recovery.

Figure 4 defines the Preamble word in OOK and FSK modulation. Preamble content must be carefully defined in

order not to be decoded as an ID or Header word.

Figure 4: Preamble definition

The Header word is a 4 bit Manchester coded message ‘0110’ or its complement sent at the selected data

rate. This bit sequence and its complement must not be found in the sequence preamble and ID word.

Data must follow the Header without any delay.

Data are completed by a End-of-Message (EOM) word, consisting of 2 NRZ consecutive ones or zeroes.

Even in case of FSK modulation, the data must be completed by a EOM and not by simply stopping the RF

telegram. If the complement of the Header word is received, output data are complemented too.

0

0

0

11

1

0

Original data

Manchester coded

OOK Modulation:

‘0’ Manchester

at data rate

‘1’ NRZ > 200µs

i.e.:

2 ‘1’ NRZ at 9.6kBd,

1 ‘1’ NRZ at 4.8kBd

AGC settling time

Clock recovery

ID

FSK Modulation:

Data slicer reference settling time

ID

3 ‘1’ or ‘0’ Manchester

at data rate

‘1’ or ‘0’ Manchester

at data rate

Clock recovery

Freescale Semiconductor, Inc.

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