V4 PWM firmware update

**mx270a** · 01-10-2009, 10:28 PM

Here is what 2k1 posted, which is what my code is based on.

Digital Outputs
2 bytes per output
[PPPPPPPS][TTTTTTMM]
P = Value of PWM
([7bit Value + 1]/128)% duty cycle
Details of full period to be determined later
S = 1bit state
0 = Off
1 = on
T = 6bits of Timer to shutoff --> [Evaluated Units in Seconds]
If 6'bTTTTTT is 0, then shut off immediately on disconnect
If 6'bTTTTTT is between 1 and 10 inclusive, then wait [6'bTTTTTT] seconds after disconnect
If 6'bTTTTTT is 11, then wait 30 seconds after disconnect
If 6'bTTTTTT is 12, then wait 60 seconds after disconnect
If 6'bTTTTTT is 13, then wait 90 seconds after disconnect
If 6'bTTTTTT is greater than 14, then wait ([6'bTTTTTT] * 10) seconds after disconnect
M = 2bit Output Mode
2'b00: Normal Full-Off or Full-On Operation Mode
2'b01: Pulse Width Modulation Operation Mode
2'b10: Yet to be determined
2'b11: Yet to be determined

The slider controls P (0-127, default is 127)
The button control S (on or off, default to off)

If the slider did everything, the button would be pointless. The only reason for the button is so you can leave the slider set on some value, and toggle the output from completely off to on for the PWM value.

Obviously the first byte doesn't work as originally documented, so how does it work? You tell me how it works, and I'll fix my code accordingly.

**mx270a** · 01-11-2009, 10:23 AM

After a little more experimentation, here is what I find:

I tried using all 8 bits for PWM, and that didn't work right. The LED would get brighter and dimmer while slowly sliding the slider bar from one side to the other. When I just use the first 7 bits, it the LED brighness changes smoothly, as it should.

The 'S' bit in the above byte spec confuses me. When 0, it appears the slider determines the PWM of the port. When 1, the LED is just full on, without any PWM.

The 'MM' bits in the above spec also don't seem to do anything. It looks like the outputs are always in PWM mode, even if those bits are set to 00, meaning full on/off mode.

**greenman100** · 01-11-2009, 01:04 PM

yup, that's right.

that's how i understood nick to want it via conversations with him.

when he gets back, we can tweak as neccessary.

**mx270a** · 01-11-2009, 01:51 PM

New version of FBDemo released.

**mx270a** · 01-18-2009, 04:00 PM

greenman, have you ever made any progress on the timers? I'd like to see the outputs shut off when data quits flowing to the FB.

**2k1Toaster** · 01-21-2009, 05:07 PM

MDX PWM code added to first post

**GadgetBandit** · 01-23-2009, 10:10 AM

I'm embarrassed by this display of ignorance, but I'm still at on/off for outputs. What are some real world applications for PWM?

Thanks,
GadgetBandit

**mx270a** · 01-23-2009, 10:25 AM

The Simplest is to adjust the intensity of lights.

If you're only using relays, it's not very useful.

I'm planning to control a proportional hydraulic valve with a PWM output. The way these work is that a 50% value is neutral, and as the PWM % increases or decreases, the valve will open in that direction by an adjustable amount. It allows me to control the speed and direction of the oil flow all from one output.