Steve,

On the frequency generator there is two output connections. One is just called output, and the other is ttl. Initially I tried the ttl but I could not pick up a signal (I should say that in the 8051 code I have a signal detect routine - it outputs 'no signal detected' when applicable) then I tried the one called output and pressed the square wave button.
As a next step I hooked the acceler. to the oscilloscope - the voltage for a one was 3.6volts and ovolts for 0. the freq of the acceler is 400 Hz. Next I set the frequency generator to mimic the acceler i.e. freq at 400Hz and 3.6 v. I also regulated the dc offset so that the low of the square wave of the freq. gen. was at ground and not below.
Now I tried the freq. gen under these conditions and the 8051 picked up the signal. Next I tried the acceler but it would not pick up a signal. Then I probed both while connected to 8051 board. The acceler voltage had dropped to about 1v for some reason, the freq. gen. doesn't drop. So I then tryed both a schmitt trigger and afterwards an inverter to give me a clean 5v out and still all failled. I guess this is why now I am wondering if p0.0 can detect an analogue sigal but not a digital one - what do you think. Thanks in advance for any light you may be able to shed.

Regards,

Seamus.