Dan Michaels says:
"Math-Averse, Stupid Guy's, Hi-Speed 8-Channel PWM"
Use a lookup table.
The uC can't do anything else when it's running, and you may get a fairly-long pause every time you change one of the 8 duty cycle values, since you have to reload or recalculate the entire table.
On a 20 Mhz PIC, you could get rock-steady 8-channel PWM at maybe 1-2 usec/step, or 1953-3906 Khz for 256 steps.
Or switching to a 50 Mhz Scenix SX18, you can get rock-steady *7* bit 8-channel PWM at 200 nsec/step, or 39,062 Khz - limited to 7 bits since SX RAM = 128 bytes.; (send block to port B - 10 clocks/loop = 200 nsec). send_block jmp :L3 ; jump to re-start (initialization). :lp1 nop ; can insert code here for bailout. nop nop :lp2 setb FSR.4 mov w,IND mov rb,w incsz FSR jmp :lp1 ; jmp takes 3 clocks on SX. ; (reload - re-entry takes exactly 10 clocks). :L3 mov w,#bufstart mov FSR,w jmp :lp2
[sorry to inject heretical scenix code into the PIC universe].
Better yet, you can easily spread the PWM energy evenly over the period, to minimize external circuitry hassles. Better yet - no need to jump into FPGA technology, if you aren't already there.
|file: /Techref/scenix/lib/io/osi1/pwm/rampwm.htm, 2KB, , updated: 2008/2/11 16:34, local time: 2020/6/2 10:18,
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