digital to analog conversion

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Danilo NASCIMENTO
Danilo NASCIMENTO 2013-10-25
评论： Walter Roberson 2013-10-26
I performed a serial communication between dsPIC33F and Simulink. When I send a constant value through serial connection to microcontroller and takes it back to Simulink, the signal comes like a train of pulses with amplitude equals to the value of the one I chose to send. I was thinking of a workaround to put a Digital to Analog converter before I send the value to serial. But I did not find any block in Simulink library that can perform this, only Analog - Digital conversion, that, I guess, will not work. I'm sending the output of signal that I received from serial connection. If anyone has a workaround for me I would appreciate.

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Walter Roberson
Walter Roberson 2013-10-25
Analog signals cannot be sent to serial ports.
Serial ports do not send constant values: the protocol is an asynch protocol with a "start bit" and a "stop bit" (one of which breaks the other portions of the protocol), and between 7 and 10 data bits (up to 12 data bits in some variations.)
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Danilo NASCIMENTO
Danilo NASCIMENTO 2013-10-26
So the PWM signal will be sent to AN0, for example, but how do I send this to Simulink Model? Wouldn't it be through serial connection?
Walter Roberson
Walter Roberson 2013-10-26
编辑：Walter Roberson 2013-10-26
Are you asking how to return back to Simulink a simulation of you having sent the signal to AN0 ? If so then that is not something I have ever looked at.
I could imagine doing it through serial transmission, by mapping the state at a fixed time step (my "unit" above) to a bit, and transmitting groups of 8 bits, with a serial receive block converting the bits into some form appropriate for the model.
Is the idea to have Simulink plot the pulse-train? If so then that can be done by having the serial receive block pass through a logical demux block (that might be implemented as an arithmetic block or two), and then on to a scope. All done in software with digital signals. You cannot transmit an analog signal directly back into Simulink over a serial port.
Another approach would be to connect the 33f AN0 to an A/D receive block on the Simulink side (i.e., have A/D hardware there), and then connect the A/D receive block to a scope.

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