COMMUNICATION PROTOCOL

MOTOROLA

MC33591 Technical Data

5

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

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.

For More Information On This Product,

Go to: www.freescale.com