Timers perhaps?

[Doormatt]

Here's one that's got me scratching my head so far.

I'm interfacing to an LED PWM chip that (as part of the display routine), needs a constant pulsetrain fed to one pin, and on a second pin, one pulse for every 4096 pulses of the first pin.

Now, the first part is easy, as I just enable clkout, and feed that to the chip. However, the second part is throwing me. I'll be the first to admit that the whole timer concept kinda throws me, but I have a feeling that's where the solution to this lies. I'd really like to avoid interrupts if at all possible, as it adds to the overhead, but if that's how this cat must be skinned, then so be it.

Here's my test code...it's cobbled together from sources, so don't nail me to the wall (please) if it really doesn't make sense.

@ device pic16F648A, intrc_osc_clkout, mclr_off, protect_off, lvp_off, wdt_off
DEFINE OSC 4
TRISB = 0 ' Outputs on
CMCON = 7 ' Turn all comparators to fully digital (needed??)
OPTION_REG = %10000011  '$84 assign prescaler to TMR0, set prescale xxx0PPP
TMR0   =  2            'add 2 to timer if you're anal about it starting exactly on the 1st cycle
INTCON = %10100000      '$A0 enable TMRO interrupt
pause 20


on interrupt goto clkreset
INTCON = %10100000      '$A0 enable TMRO interrupt

start:
goto start

clkreset:
    PORTB.7=1
    PORTB.7=0
    TMR0 = 2   'correct timer for missed cycles?
    INTCON = %00100000 '$20 Reset interrupt set T0IE, clear T0IF
resume

And so I'm (hopefully) clear, here's what the code would look like if I didn't need it to run in the background constantly.

start:
    for I=0 to 4095
        PORTB.7=1
        PORTB.7=0
    NEXT i
    PORTB.6=1
    PORTB.6=0
goto start

-Matt

[skimask]

An idea that might be even easier for you...

'setup code...
counter var word

main:
counter = counter + 1
portb.7 = counter.0 'portb.7 toggles at the rate of the LSB
portb.6 = counter.12 'portb.6 toggles at the rate of the LSB/4096
pauseus xxxx 'add your pause to get the rate down
goto main

The loop will always execute at the same speed.

[Doormatt]

Very interesting!

But sadly enough, I can't use it. I need the PIC to generate these two clock pulses independently of the rest of my program. The second chunk of code I had was just an example of what I need to accomplish.

I'm still reading, and from what I garner, I need to set the prescaler on one of the timers, and trigger it from the internal clock...or something to that effect. I'm honestly quite confused at this point.

Thanks for the bit trick there though! VERY cool!

[skimask]

Very interesting! But sadly enough, I can't use it. I need the PIC to generate these two clock pulses independently of the rest of my program. The second chunk of code I had was just an example of what I need to accomplish. I'm still reading, and from what I garner, I need to set the prescaler on one of the timers, and trigger it from the internal clock...or something to that effect. I'm honestly quite confused at this point. Thanks for the bit trick there though! VERY cool!

How fast does that bit on portb.7 have to toggle? What freq do you want?

[Doormatt]

Let's abstract for a sec.

I need two pins, call them A and B.

If Port A is pulsing at 4096Hz, then Port B needs to pulse at 1Hz. (In the real world, Port A needs to be a minimum of 245Khz)

But, I need to do this in the background.

Ideally, port A would be driven by the clock out, and port B would pulse once for every 4096 pulses coming out of the external clock.

Does that make more sense (sorry if I'm being confusing!)

-Matt

[skimask]

Let's abstract for a sec.
I need two pins, call them A and B.
If Port A is pulsing at 4096Hz, then Port B needs to pulse at 1Hz.
But, I need to do this in the background.
Ideally, port A would be driven by the clock out, and port B would pulse once for every 4096 pulses coming out of the external clock.
Does that make more sense (sorry if I'm being confusing!)
-Matt

Ok, so you need the fast pin at 4096Hz and the slow pin to pulse at 1Hz? Yes?
Is that what you actually need?
It is definitely a doable project, interrupt driven pulses and all...just need to know your exact numbers.

[Doormatt]

Yay!

It's doable!

I need One pin at a minimum of 245Khz, and then the other pin at a 1:4096 ratio.

As long as that one pin is over 245Khz, I'm happy.

(Detail warning)
Basically, the chip I'm controlling has 16 PWM outputs, each with 4096 brightness levels. You serially clock in your data, and then feed it the aforementioned pulse train. That pulse train makes it step through the brightness levels, and then the single pulse resets the display chip. I need a minimum of 247Khz, as I have to update the display 60 times a second, and with 4096 levels, thats 60*4096Hz = 245Khz.

Thanks SO much for helping me with this!