[msp430] problem with digital input

[michal_w]

Hello,
I have to measure sine wave (voltage between 0 and 2.5 V) using analog-ditigal converter. The measurement should be synchronized with the transition by zero (square wave 0 and 3.3 V detected by digital input/output - more here).
I'm using uC MSP430F149 - sine wave is connected to ADC input (P6.0) and square wave to Port 1 (P1.0).
Every single circuit works perfectly well, but the proglem occurs when I connect both circuits in the same time - P1.0 input is always in high state.
It seems the sine wave is added to square wave.
Could anyone tell me what should be done to make my circuit working?

Thanks in advance - Michal.

 

[alec_t]

Have you double-checked that the input pins are correctly configured for digital/analog as appropriate?

 

[michal_w]

Pin configuration:

P1 (square wave input)
P1DIR = 0 (input)
P1SEL = 0 (digital i/o)

P6 (ADC):
P6DIR = 0 (input)
P6SEL = 1 (peripheral module)

 

[alec_t]

That looks right. So maybe the impedance between the two inputs is low at the frequency being used. What is the frequency? Is the circuit built on a custom pcb, or a breadboard, or....?

 

[michal_w]

The frequency is 50Hz. PCB with MSP430 is a development board made by scientific group.
Schemes are in attachements.

 

[alec_t]

Signal breakthrough at 50Hz is unlikely to be a problem, then, if the pcb has been properly designed and populated. I've run out of ideas. Perhaps someone else has some insight?

 

[michal_w]

Hello,
it turns that I incorrect pins was connected to MSP. I've fixed thatbug and now it works.
Thanks for trying to help and sorry for unnecessary thread.

Michal