ctra and ctrb

mikea · 2015-02-17 15:32

Hi, I'm trying to scale 2 of the 3 pins of an rgb led with ctra, and ctrb. I have code that works from the pe kit for ctra in the first 255 to 0 loop which works great except pin 5 (ctrb is always on). The second loop for pin 5 using ctrb results in both pins 4 and 5 on, but no scaling. I was trying to scale them one at a time. I've read the section of the prop manual about counters, but not sure where I'm going wrong. It looks like for the third led I need to open a new cog for more counters. Thanks

CON
        _clkmode = xtal1 + pll16x                                               'Standard clock mode * crystal frequency = 80 MHz
        _xinfreq = 5_000_000

''LedDutySweep.spin
''Cycle P4 LED from off, gradually brighter, full brightness.
scale = 16_777_216 ' 2³²÷ 256
PUB TestDuty | pin, duty, mode
'Configure counter module.

ctra[30..26] := %00110 ' Set ctra to DUTY mode
ctra[5..0] := 4 ' Set ctra's APIN
frqa := duty * scale ' Set frqa register

ctrb[30..26] := %00110
ctrb[14..9]:=5
frqb := duty * scale

Use counter to take LED from off to gradually brighter, repeating at 2 Hz.
dira[4..5]~~ ' Set P5,4 to output
repeat ' Repeat indefinitely
   repeat duty from 255 to 0 ' Sweep duty from 0 to 255
     frqa := duty * scale ' Update frqa register
     waitcnt(clkfreq/128 + cnt) ' Delay for 1/128th s 
     
  repeat duty from 255 to 0 
     frqb := duty * scale 
     waitcnt(clkfreq/128 + cnt)

JonnyMac · 2015-02-17 15:42

I haven't found direct control the counters (i.e., outside a control loop) useful for LED control. The reason is that you only have control of duty cycle, not frequency, and when the duty cycle is near 50% the frequency is so high that there is sometimes not enough time to properly light the LED. I would suggest you create a Spin cog that allows you to control the counters at a specific frequency. Launch this twice and you can control four LEDs.

ChrisGadd · 2015-02-17 16:30

You've got pin 5 assigned to counter b's b-pin rather than the a-pin. The B-pin output doesn't have any use in single-ended duty mode. Change ctrb[14..9]:=5 to ctrb[5..0]:=5, just like you set up counter A.

Do you have the outputs connected directly to the LED? I tested this using a generic red LED and it worked, though the brightness seemed to change rather abruptly in a few places. Using a low-pass filter to create a digital-to-analog converter resulted in a much smoother transition, though the range was also reduced somewhat.

mikea · 2015-02-17 17:15

I do have the outputs directly connected to leds through a resistor. Thanks for clearing that up with the b-pin, I changed [14..9] to [5..0] and it worked.

JonnyMac · 2015-02-17 18:00

It will be interesting to see how the LEDs respond -- they might work just fine. In practice I wasn't happy with direct control so I used a code loop to provide freqency AND duty-cycle control (it takes a cog but it's worth it).

If you have a cog to spare, here's a very simple embedded RGB LED controller. Paste this into your program and then call start_rgb() with your pins.

var

  long  rgbcog
  long  rgbstack[16]
  
  long  red
  long  green
  long  blue


pri start_rgb(rpin, gpin, bpin)

  if (rgbcog)
    cogstop(rgbcog - 1)

  rgbcog := cognew(run_rgb(rpin, gpin, bpin), @rgbstack) + 1


pri run_rgb(rpin, gpin, bpin) | racc, gacc, bacc

  dira[rpin] := 1
  dira[gpin] := 1
  dira[bpin] := 1

  repeat
    racc += red                                         ' update accumlator
    outa[rpin] := (racc > 255)                          ' move carry to output
    racc &= $FF                                         ' clear carry

    gacc += green
    outa[gpin] := (gacc > 255)   
    gacc &= $FF

    bacc += blue
    outa[bpin] := (bacc > 255)   
    bacc &= $FF

ctra and ctrb

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