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Why do the ON and OFF times are inverted when using PPG output?

Latest Updated:04/01/2006

Question:

I want to have a fixed frequency and vary the duty in the uPD78F0034A, but sometimes the ON and OFF times are inverted when I check the waveform using PPG output.

Answer:

There is probably a problem with the timing of writing to CR01.
The output of Timer 0 inverts upon a match with CR00 or CR01.
Therefore, if CR01 is overwritten by a larger value after it is matched, a second match with CR01 will occur in a single cycle, causing the output to invert again, returning to the original value.

Alternatively, when the timer value is smaller than CR01, if a value that is smaller than that timer value is written, a match with CR01 does not occur in that cycle, so matches will occur continuously with CR00. As a result, the output state inverts.

Also refer to the FAQ "No PPG output" immediately below.
Suitable Products
78K0/Dx
78K0/Fx
78K0/Ix
78K0/Kx
78K0/Lx
UPD78F07xx
UPD7800xx
UPD7802xx
UPD7803xx
UPD7807xx
UPD7808xx
UPD7809xx
UPD780xx
UPD78F8025
78K0/VAN ASCP