1) I'm making a wireless TX/RX system with and LED and photodiode. On one side I'm using the PIC16F15313 to blink an LED at 10Hz for 100uS each blink and I'm also using the PIC16F15313 to turn on a receiver that is looking for the blinks on the other side. It needs to be low power since it will be battery powered so the PIC will turn off between blinks (ideally), but the timing is very important so I'm wondering if I should consider an external oscillator to keep a more accurate time of when to blink, how long to blink for, when to sleep, and when to wake up. What would I look for in the datasheet to understand the variation in time between using the internal oscillator VS an external oscillator. Would be nice to know that over a wide temperature range too. The datasheet says the internal oscillator is "factory calibrated" so maybe it's good enough, just would like to know for sure.
2) Why is a PIC16 core an 8-bit and not a 16 bit?