I am connecting a sensor that has a 3.3V output to an STR7 TTL input (via a breadboard). If I disconnect the sensor from the breadboard, I see that its output level swing to 3.3V and falls to 0V as expected. But the STR7 input, if connected to the sensor, only allows the sensor voltage to rise to about half the need value - 1.56V. The input is configured like this:
GPIO_Config(GPIO0, 0x0001 << 0x0F, GPIO_IN_TRI_TTL);
There are exotic things in between. What am I missing?
Thanks
Thanks. If I connect the sensor to pin 1.14, the voltage _does_ rise to 3V3. The data sheet says that P0.15 is of type TTL 0.8V/2V while P1.14 is of type CMOS 0.3Vdd/0.7Vdd but I don't see how that is related. I will look further.
You don't think a processor pin designed for 2V operation clamps overvoltages to protect it? Most digital CMOS pins clamps overvoltages.
I see that the TTL input indeed clamps the voltage, but the CMOS input does not. Why?
You sure the CMOS input doesn't clamp too - if you go above the supported voltage 3.3V?
The CMOS input does not clamp the voltage, but the sensor never exceeds 3V3. Well, as long as it is clamped by P0.15 I cannot use it (not a big deal to be honest) because the microcontroller never detects 1.56V as "logic 1" (input is used as a wake-up from low power mode...). I will try to set P0.15 to input mode at the beginning of "main()" and see what voltage levels are reached. Maybe it is something in the software, after all.