Gear Tooth Pulse Height ??

[Dave K.]

Originally Posted by Lloyd Burns

If you are going to a digital input (no an analog one), they typically require more than 2 V for reliable operation. If the input is typical CMOS (not TTL or TTL-compatible CMOS), the figure is 'more than half of the internal supply voltage'. I haven't taken apart a new RC, but that is probably 5 V, meaning around 2.5 volts.

Table 1-4 in the microcontroller datasheet details which pins are Schmitt trigger inputs, and which one's are TTL. Cross referencing the digital I/O definitions found in 'ifi_aliases.h' will provide the information as to which I/O pin corresponds to which pin on the CPU.

Section 28.3 of the datasheet details the minimum logic thresholds for each pin type.

Maximum Logic Low voltage:

TTL: 0.15Vdd (0.75V)
Schmitt: 0.20Vdd (1.0V)

Minimum Logic High voltage:

TTL: 0.25Vdd + 0.8V (2.05V)
Schmitt: 0.8Vdd (4.0V)


Thus, User I/O pins 1 and 2 (RB2 & RB3) would use Schmitt logic thresholds when used as interrupts. User I/O 3-6 (RB4-7) would use TTL logic thresholds for the interrupt-on-change inputs.

The other user inputs vary in type.