AN2708 datasheet(24/42 Pages) STMICROELECTRONICS

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DALI master unit

AN2708

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DALI master unit

The ST2C334J4 microcontroller is used as master, implementing the DALI Peripheral via

software.

The communication master-slave uses a 20 V bus. To adapt the TTL level of the

microcontroller to the communication bus level, two opto-couplers and a NPN transistor BC-

817 have been used.

The RS232 interface with ST232C is available on the board to implement the SCI

communication as an option. This option expects the use of a PC to address the ballast

either with broadcast or group or single mode thanks to a GUI called (DALI Power Control).

The DALI master unit has been thought of as a standalone solution. In fact it is provided

with a keyboard to manage the DALI commands, to address the slaves and to display the

lamps’ status.

The keyboard is made up of 16 push buttons controlled by means of a matrix

representation. In particular the first four pins of PORTD are associated to the rows and the

first four pins of PORTB to the columns.

The check of the keyboard is implemented as a loop mode by clearing the PDDR register

port and setting the PBDR register port sequentially. When a button is pressed, the pin of

the port B corresponding to the interested column goes down and this condition is taken

over by an interrupt condition. Inside the interrupt routine, a read procedure of the port

registers PDDR and PBDR is expected and by this information the pressed button is

acknowledged. The “press button” procedure is described by Figure 17 and 18.

Figure 17.

Polling keyboard

CH1 (yellow): row polling

CH2 (purple): column level

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