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IRPLDIM2U

Isolation and the Signals for DALI

The Digitally Addressable Lighting Interface is optically isolated from the microcontroller. Fig. 7 shows the connec-

tions between DALI and microcontroller.

The two wires from the DALI are converted to four signals. Two of the four are the transmit signal (RB2) and

receive signal (RX_DALI). The other two signals are the communications-enable (RB0) signal and the receive-

drive (RB1) signal. The transmit signal and the receive signal directly correlate to the levels seen on the Digitally

Addressable Lighting Interface. For receiving higher voltage logic on the DALI is translated to 5 volt logic at the

micro controller, and for transmission, the 5 volt logic is translated to the higher voltage logic on the DALI.

The ballast achieves very low power by controlling the communications circuit with the communication-enable

signal and the receive-drive signal. During normal operation the PIC16F628 enables the communication circuitry

with the communication-enable signal. With this signal there is enough current, less than 100uA, to indicate when

data is being sent to the ballast, but not enough current to accurately transfer the data. Upon detection (done by

a S/H built into the PIC16F628) the receive-drive is asserted to raise the current above 500uA to achieve good

signal transfer across the isolation. The receive-drive signal is only enabled long enough to transfer all the data;

then it is disabled (see waveforms in figure 8). This method strongly reduces the power/current use. The com-

parator built into the PIC16F628 is used to set the threshold for detection of the incoming data. The signal RA2 is

used as threshold for the comparator.

+

-

DALI

ENABLE

RB0

TX_DALI

RB2

RECEIVE-DRIVE

RB1

RA1

RA2

RX_DALI

MICRO-CONTROLLER

Fig. 7 DALI and Micro Controller connections