Electronic – COP8 MCU information needed

If the pins have clamp diodes, you need only a series resistor to limit the current. You can see in the application note AN521 from microchip that it connect the pin of the microcontroller directly in the AC.

I have used a voltage divider to connect a PIC to a GPRS module with a speed higher than 19,200 and had no problem.

You ask for "context saving", but you don't seem to know what that term means in your context?

The meaning I am most familiar with is in the context of interrupts and task switching, where everything that the main program or a task relies on is saved in RAM, to be restored later. In most cases this amounts to pushing all registers on the stack, so they can be popped later.

Things can get difficult when there is context outside the CPU registers that can be used by the interrupt (or by other tasks), so it must be saved too. Think for instance of floating point coprocessor registers.

On a the old 12 and 14 bit core PICs context saving for an interrupt is a bit tricky, but it is explained in the datasheet, better read it there. Note that on these chips various memory-mapped registers can be context too, like the indirection register. If your interrupt routine uses such registers they must probably be saved (and restored) too.

Real context swapping for tasking switching is not possible on these PICs, because the stack can not be changed. There are some dirty tricks that achieve the same effect (like not using the hardware stack at all), but at a cost.

The 18F PICs and IIRC the enhanced midrange chips too have a stack that can be read and written, so real context switching is possible, but it is tedious. If you want multitasking, better look for a CPU that has a memory-mapped stack. (Nowadays a Cortex would be an obvious choice.)