===== Tachometer =====

VDO: 0.5--999 pulses/rev

Target 0.5--4 pulses/rev

Max 20,000 rpm = 333 rev/s -> 167Hz--1.332 kHz max

Target resolution: 100 rpm. Target max: 20,000 rpm. 20,000/100 = 200 = resolution. Need 8 bits.

PIC16F1459 PWM min frequency with PR2=0:
f = FOSC / (4 * TMR2_prescale)
f_min = 48e6 / (4 * 64) = 187.5 kHz
With 10-bit clock divider (counter): 187.5 KHz / 1024 = 183 Hz
Just above target max frequency of 167 Hz.

TMR0
Use TMR0 for control.
3-bit prescaler 2--256
Min frequency without using TMR0: f = FOSC / (4 * pre)
f_min = 48e6 / (4 * 256) = 46.9 kHz

Alternative to hardware clock divider: software counter.
Increment on timer interrupt.
When reaches threshold, toggle pin.
Uses more CPU cycles but less board space and money than hardware clock divider.

TMR1
Can use with LFINTOSC, FOSC, FOSC/4, or external 32.768 kHz oscillator.
LFINTOSC = 31 kHz.
Pre = {1, 2, 4, 8}.
Without using TMR1H/L: f_min = LFINTOSC / 8 = 31,000 / 8 = 3.875 kHz
Use for both tach and speedo, each with their own software counter?
Then can use TMR1H/L to divide frequency further and use software counters for independent control of tach and speedo.
Use TMR1H/L to divide frequency, and Pre to set pulses/rev? Can't use for both tach and speed then.

TMR2
Use PR2 for control.
f = FOSC / (4 * pre * pr2 * post)
pre = {1, 4, 16, 64}
post = [1,16]
Without PR2: f_min = 48e6 / (4 * 64 * 16) ~= 11.7 kHz


===== Speedometer =====

Stack: 310--248,500 pulses/km

Target 320 km/h = 320/3600 km/s
f = 27Hz--22kHz min/max

8-bit resolution is OK.

Use TMR2 for speedo.
Outputs min 11.7 kHz without using PR2.
Don't need software counter.

Then can use TMR1 for tacho.