New to PIC's and not having a degree in electronics, I have a question:

I want to drive an ultrasound transmitter (pi=EBzo, 40 kHz) directly =
from picpins. I tested this using the PWM on a 877A. The transmitter is =
connected between the pwm-output and Vdd. This produces a very good =
ultrasound sinewave.

Next, to increase the transmitter's output, I connected the transmitter =
between RD0 and RD1 on a 18F452 running at 40Mhz and wrote some code to =
generate a 40kHz block. I toggle both pic-pins in a single cycle in an =
attempt to create a pure wave as much as possible. This means that one =
pin goes from sinking to sourcing and the other pin going from sourcing =
to sinking in a single 100ns cycle. This did not work a I expected. =
After some more experimenting using the scope, I came with the following =
explanation:

What I am doing asks to much from the pins as pin switching-times for =
sourcing to sinking is not equal to the time from sinking to sourcing. =
Furthermore, the timings on the pins are not necessarily equal on both =
pins (probably they are not). This results in effectivily shorting Vdd =
to Vss for a very brief moment through both pin-drivers.

Is this assumption correct? What timing should I use to do the toggling =
safely? Is seperating the toggle into two instructions enough?

Thanks,

Marcel

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