Posted 24 August 2011 - 05:00 AM
Good point, Fabien.
We should be aware (in general) from circuits using old CMOS chips, because they have serious limitations compared to the more modern HCMOS tech (which Netduino is).
The old CMOS tech is very slow: 1-2 MHz, and the shape of the digital patterns are yet distorted. This limits very much the speed of other logic, even faster. The poor bandwidth could also lead to wrong data levels, due the slowness of the rise/fall edges.
Another problem is the high stray capacitance of the CMOS inputs. When you play with leds or buttons this capacitance has no importance. The problem could arise when you connect the output of a high speed logic (such the Netduino SPI) to an input. The high frequency of switching between levels causes an excessive current flowing through the CMOS input, due the capacitance.
For the Netduino world, there are very few cases where a CMOS chip could be preferred over a HCMOS one.
I may cite just one, for completeness: the ability of the CMOS chips to work up to 15V, make them a considerable way for level shifters or similar. However, the speed involved must be relatively low.
Biggest fault of Netduino? It runs by electricity.