B&B Electronics Asynchronous to Synchronous Converter 2010 Manual do Utilizador descarregar pdf (Página 18)

Department of Computer Science and Electronics

4. Design

4.1. Analysis of problem

In figure 4-1, we have a general circuit. The three cards as well as the PPC are

connected to the RS485 network. The three cards are identical to each other so each one

has eight sensors and an Atmega16 microcontroller. The Max 489 is a transceiver; it

connects the microcontrollers to the RS-485 network.

The microcontroller can do 2 basic things:

1—Calibrating: this means calculating each sensor’s threshold.

2—Sends the sensor’s state digitally to the PPC, i.e. in the form of a logical 1 or 0.

Any action taken by the microcontroller is a result of a PPC’s order. The PPC is

sending messages to the RS485 network. The structure of the data frame is illustrated in

figure 4-2:

Figure 4-1. General diagrame

AddressÆ 0:3

7th 6 5 4 3 2 1 0

xxx

1: calibration

0: send data to PPC, no calibration

Start bit

Stop bit

Figure 4-2. Order’s location in the frame

1 2 ... 13 14 15 16 17 18 19 20 21 22 23 ... 42 43

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