frequency of pwm on 20 mhz crystal
Mr.Cool said:
i decided to go with the PIC chip method and drop the 68HC11 all together. the pic chip of choice is the 16F877 with 20MHz crystal. with a prescalor of 1:2 (is this the smallest?) i get an E-clock of 10MHz. this is some 5 times more fast than the 6811 with a 2MHz E-Clock.
therefore, my max PWM speed should be 15KHz * 5 = 75KHz.
goal achieved
my only problem now is that PIC chips are hard to learn!!! BANK1/0 memory, what's that~!? hahaa
Mr.Cool
1. HC11 with 2MHz Eclock can generate in best case 7.8125kHz PWM
output with 8bits of resolution, not 15kHz. + It hasn't hardware PWM
generator -so it's difficult to generate outputs for near to minimum and
maximum output values. 2kHz sounds more real.
2. Max PWM source clock for 16F877 (20MHz crystal) is 5MHz and for
8bit resolution you can get 5e6/2^8=19531.25Hz Max PWM frequency.
For 60kHz PWM you can get 5e6/60k=83.3 max PWM period value
or 6-7bits of resolution. No way to make it better. Can you
overclock PIC16F877 to 61.44Mhz crystal clock(15.36MHz bus clock)?
I don't know if Scenix has hardware PWM. If no for software
PWM 8bits*60kHz it should have 20-30MHz of busclock if you want
full range of output 0..255.