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Applications Building a MPC555-Based Oscilloscope
by Daniel Mihalik

Start ı Software Description ı Oscilloscope Operation ı Enhancement Opportunities ı Sources and PDF

OSCILLOSCOPE OPERATION

In order to use the oscilloscope, two programs are necessary, the C program on the MPC555 and a program on the PC. If possible, download the compiled executable files. First, compile the included file scopelab.c and load it into the internal RAM or flash memory on the MPC555 using your preferred software. Second, execute the file scopelab.exe in Windows on your PC. Photo 1 shows you what will appear.

(click here to enlarge)

Photo 1ıWhen the Visual Basic program starts, youıll see an empty graph with four buttons at the bottom.

Use the buttons as described in Table 1. The graph of a sample triangle wave input is shown in Photo 2.

Button	Description
Receive	Tells the MPC555 to start sampling the pin AN0 and the PC to receive the points over the serial port
Graph	Graphs the sampled voltage at AN0 over time. (If no graph appears, the receive transmission has not finished. Wait a few seconds and click Graph again.) To overlay new points, press Receive and then Graph again.
Clear	Clears the graph window
Save	Saves the most recent set of points as a *.csv file. This file can be opened in most spreadsheet programs.
Table 1ıThe buttons in the program are used to obtain and manipulate the data points from the MPC555.

(click here to enlarge)

Photo 2ıThe oscilloscope can capture signals with a maximum voltage of 5 V. Shown is a 5-V peak-to-peak triangle wave with a frequency of 2 KHz and an offset of 2.5 V.

As mentioned earlier, the oscilloscope can be run without the Visual Basic front end. Youıll need a terminal emulator program with the capability to capture text to a file. First, open the terminal program with the settings 9600 bps, no parity checking, start bit 8, and stop bit 1. Run the program on the MPC555 and start the connection in the terminal. Start the text capture, then press "s". Stop the text capture when the data stops. Save the file as *.csv.

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