delays for nano seconds?

[greentech]

how can i generate delay for nano seconds in flowcode?

[brandonb]

other members please correct me if im wrong, i dont think you can because of the clock speed limitations, at 32 Mhz clock it takes 1 microsecond to turn a output on and off, at 4Mhz it takes 8 microseconds thats straight time without any delays

[Mikat]

other members please correct me if im wrong, i dont think you can because of the clock speed limitations, at 32 Mhz clock it takes 1 microsecond to turn a output on and off, at 4Mhz it takes 8 microseconds thats straight time without any delays

Yep, Brandon are right, but you can have 1 instruction cycle delay with asm nop command (thats 100ns@40MHz chip clock)...

[greentech]

i am trying to drive a chopper transformer for switching supply. what do u advice?

[Benj]

Hello,

the dsPIC 33 family can run up to 40MIPs so one 16-bit instruction every 25 nano seconds.

What kind of resolution are you looking for?

[greentech]

benj all i want is to drive a soft ferrite transformer, or u can say 12vto48v dc-dc converter for charging batteries from solar energy.
i am confused about the frequency on which chopper works.

[Mikat]

Hi.

Isn't that easier done at hardware pwm?
At dsPic30f you can get 300KHz pwm at 1% resolution ( I am not an expert, but is there any reason to use very high switching frequency, it just rises the switching loss)...

Mika

[greentech]

i guess i need only 2 - 20 khz switching. how can i do that by pic16 devices?
when i put a delay for micro seconds, on scope it shows time for milliseconds....whats going wrong there?

regards.

[brandonb]

did you set up the clock frequency in (build,project options) the same as your osccon register c block (if applicable)

[Benj]

Hello Greentech,

Use the 1 second flasher test to confirm you have everything setup correctly.

eg

while(1)
{
output 1 to LED pin
delay 1s
output 0 to LED pin
delay 1s
}

When the delays on the hardware match 1 second you have the Flowcode clock speed and configuration settings setup correctly for your hardware.

[greentech]

Checked it benj, all woking fine except for the pulse delay is in milliseconds when i hook it to scope. I am trying to get 2 pwms 180 degrees out of phase. how can i invert the pwm?

[Mikat]

Checked it benj, all woking fine except for the pulse delay is in milliseconds when i hook it to scope. I am trying to get 2 pwms 180 degrees out of phase. how can i invert the pwm?

In hardware pwm you need eccp module and set the register via c-code, if you want full or half bridge configuration, some 16f chips have the eccp module, then you can set two pwm:s at the 180 degrees phase shift (or actually one pwm, which drives two pins), and the dead band delay is adjustable too, but at least at version 4 flowcode doesn't support that.. But it's the "sure" way, that way there is hw logic to prevent switches opening at the same time...

Mika

[medelec35]

I am trying to get 2 pwms 180 degrees out of phase. how can i invert the pwm?

Hi greentech,
Same question was asked on a different thread so I posted a solution here:
http://www.matrixmultimedia.com/mmforum ... 701#p26295

The only issue will be a slight delay at the higher speed end.

Mika coved Other options which I totally agree with.

Although Flowcode does not support half bridge using ECCP, I would guess this could be achievable using C code and would be the best method if not using external components.

Another method to consider, is connect the PWM output to a spare interrupt on change input pin, then within IOC macro an output pin can be = NOT IOC input.

Martin