memorymicrochippic
MMU is needed to run Linux and perhaps for other tasks related to OS. However, the PIC32 does not have one of these. Why would someone make a high end microcontroller and not include a MMU?
It may make sense for lower level PICs like PIC18F, PIC24 to not have MMU, but why did Microchip not put in an MMU into the PIC32 which is their high end processor?
So I'm not too sure I follow this first question here, but I'll take a stab at it: if Vin = 3.3V (i.e. your P-channel mosfet does not connect source and drain) then "TRIGGER" will essentially be disconnected, yes. This assumes that "TRIGGER" is connected to a high-impedance source, like an input pin on a standard microcontroller. As a quick note "essentially disconnected" means that there is a high impedance threshold to get across the source-drain junction, but it is not infinite. If Vin = 0V (i.e. source and drain are connected), then trigger will be close to (but slightly less than) 3.3V
So an input pin on a PIC24F is high impedance. This means that it will behave like a resistor with around 1MΩ of resistance to ground. If you check the "Electrical Characteristics" section in the "DC Characteristics: I/O Pin Input Specifications" subsection in the datasheet for the chip you're using, you should find a table which gives you the "Input Leakage Current." Using the dsPIC33FJ256GP710A as an example (it was a datasheet I happened to have on my machine), it lists 0 to 3.5 μA as the leakage current into or out of a pin within the limits of those pins.
So as a note, you'll also see that in the "Electrical Characteristics" section under the "Absolute Maximum Ratings" subsection, there will be a list which says something to the effect of "Voltage on any pin that is not 5V tolerant with respect to VSS(4) .... -0.3V to (VDD + 0.3V)". This is telling you that you can't put more than ~3.6V on any pin without damaging the pin. This doesn't mean that you should put a current-limiting resistor in front of the input pin, this means you should put a voltage divider in front of the input pin to limit the maximum voltage to less than VDD + 0.3V.
To tie this into question #1: this means that when a digital input pin is connected to a high-impedance output source like Fig. 1, you will see oscillating input values (1 and 0 randomly) based on when that very small drain removes or adds enough electrons to jump from one digital state to another. This is called a floating input
So I just answered this question in the previous one, but I should tell you: the "Maximum output current" is not internally limited. So although the PIC24F can "only output 18mA" this means that if you connect an output pin which is high directly to ground, it will output lots more than 18mA before it burns out! The 18mA is the maximum it can safely output without overheating/damaging the chip. This is true for both sourcing and sinking, there is no fuse which will stop you at 18mA, only the magic blue smoke.
Just to reiterate: you can safely connect any voltage to a digital input pin within its range (-0.3V to VDD+0.3V for the dsPIC33F). It would not blow the pin to connect it directly to +3.3V, nor would it blow the pin to connect directly to ground.
Just answered this in #3, but again, it's not the output impedance of the pin which limits this... Or, more accurately, it is the output impedance, but it will limit the currently by melting.
And yes, you can safely remove the 1kΩ resistor from Fig. 2 without damaging your PIC.
You can solve this problem with just a couple of parts. TI makes logic parts in their 74AC logic family that operate correctly down to 1.5V. Use a 4 bit counter as shown below to repeatedly count from 8 to 15. Use the RCO output, which is a one clock wide pulse to reload the counter and to also drive an R/C circuit to produce the narrow pulse that you require.
If you desire to produce the pulse for every 16 input cycles then just connect the D input to GND instead of being pulled up to the VCC rail.
Best Answer
PIC32 does mot have Memory Management Unit ...
But it does.
The PIC32 uses the MIPS architecture, which normally is paired with an MMU. When Microchip designed the PIC32MX family, they left it off. The largest PIC32MX, in terms of memory, is the high-end PIC32MX795F512L which has 512KB of program flash and 128KB of RAM.
However the newer PIC32MZ family, introduced earlier this year, does have an MMU (or so the datasheet claims on the first page; I haven't used it yet).
The PIC32MZ2048ECM144, for example, has 2MB of program flash and 512KB of RAM. I'm pretty sure this is still not enough to run a real version of of Linux. In any case I'm guessing Microchip will continue to come out with new PIC32MZ versions with increasingly larger memory spaces. Ideally, they might come out with a PIC32 that has an external memory interface (appearing in the memory map as regular memory, not a peripheral). PIC32s already can run code out of either flash or RAM.
A while back I saw a job listing from Microchip for a Linux drivers engineer. Hmm.