IRPLDIM2U Datasheet, PDF (8/13 Pages) International Rectifier – Digital Dimming DALI Ballast for 32W/T8 110V input

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.
+
DALI
-
RB0
ENABLE
RB2
TX_DALI
RB1
RECEIVE-DRIVE
RA1
RX_DALI
RA2
MICRO-CONTROLLER
Fig. 7 DALI and Micro Controller connections
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.
8
www.irf.com