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Building a MPC555-Based Oscilloscope
by Daniel Mihalik

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

In this article, Iıll explain how to use the queued analog-to-digital converter (QADC) and the serial communications interface (SCI) peripherals on the MPC555 to create a simple oscilloscope. Iıve included the source code to allow you to duplicate or enhance the program. The MPC555 software captures 256 samples, one every 7 ıs, from the QADCıs AN0 pin and transmits them over the SCI to the COM port of a personal computer. The samples are graphed and optionally stored using a program made with Visual Basic.

The program is useful as a debug tool for examining the analog inputs of a MPC555 attached to a system in which the analog pins are inaccessible or an oscilloscope is unavailable. The oscilloscope firmware can run entirely in internal SRAM, so any program in internal flash memory program does not need to be altered.

The following parts are needed for this project:

• MPC555 Evaluation board or other MPC555 target
• Personal computer with open serial port
• MPC555 compiler software
• MPC555 debugger or other means to download the program to RAM or flash memory
• Function generator (optionalıthe generator is needed to see waveforms on the completed scope)
• Microsoft Visual Basic development system (optionalıOnly needed if you want to modify the program that runs on the PC.)

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