Olin, Wouter,

I understand why xoring directly to the port may cause errors and how using
the latch corrects this. Thanks!

On my scope:
Without ultrasound transmitter attached, I see a clear, sharp edged 10Vtt
block.

With transmitter attached, I have to increase the scope's sensitivity to
15mV/div to see something happening at a 80kHz rate. I assume this is the
toggling of the outputs every halfperiod (1 use 40kHz ultrasound).

I have not been able to locate any datasheet on the transmitter (MA40A5S). I
think it's a Murata part. Looking at the other transmitters at the
Murata-site I expect the capacity of the transmitter to be something between
2000 and 2500 pF. I guess one could call this hiiighly capacitive load!

I have tried to attach the transmitter between Vdd and one of the us-pins.
No luck. This is strange because using the PWM on a 16F877A produced a solid
signal when the same transmitter is connected between Vdd and PWM-out...

Next test will be to use the PWM of the 18F452. It should behave like the
PWM on the 877A, right? If it does not then, I guess, one might conclude
that the 877A pins tolerate loads with a higher capacitance than the 452.

I'll be back!

Marcel

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