AN1465

DS01465A-page 6

 2012 Microchip Technology Inc.

Manchester Encoding/Decoding

Any packet sent between the control device and control

gear is a bi-phase Manchester encoded packet. The

packet is then decoded, and the address and

messages are then processed accordingly. Our lighting

communication board has a PIC16F1947 microcon-

troller unit along with an isolated DALI communication

circuit interface and a simple power supply. Please see

“Appendix A” for the schematic details.

Since the signal from the DALI bus is inverted by the

microcontroller views the Manchester encoding/decod-

ing.

The Manchester code is a digital encoding format in

which symbol ‘1’ is represented by a falling edge (high

followed by low), and symbol ‘0’ is represented by a

rising edge (low followed by high). Both the high and

low pulses have equal width, which is equal to half the

bit period.

FIGURE 11:

MANCHESTER

ENCODING OF A BIT

Manchester Encoding

The outgoing message is encoded using Timer1, and

the packet is sent out using the RC5 pin. An interrupt is

generated using Timer1 every Te, which is 416.67 µs.

Te is the half-bit time, and this is where we want to

change the phase of the signal. If we were sending out

a ‘1’ as our bit, the first half is ‘1’ and at the interrupt the

signal is reversed and vice versa. As a result, the out-

put is a Manchester encoded packet, ready to be

decoded by the control gear if sent by the control

device, or decoded by the control device if sent as a

response by the control gear back to the control device.

FIGURE 12:

MANCHESTER ENCODING

0

bit-time

1

IDLE

IDLE

11

01

0

0

10

CLK

Signal

Manchester

encoded