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Propeller P8X32A?
08-27-2015, 12:50 AM,
#1
Propeller P8X32A?
Anyone have any experience with or input about the Propeller P8X32A? It looks like a 32-bit, 8 core, 80Mhz microcontroller in a 40-pin DIP configuration. 2kB RAM per core, and 32kB RAM global. Each core apparently has a video generator capable of VGA or composite.

I'm trying to find a downside other than it being a 3.3V chip and needing external circuitry (EEPROM/USB plug).
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09-28-2015, 01:02 AM,
#2
RE: Propeller P8X32A?
Found the downside!

If you hook up the chip like it shows in every "minimum breadboard" sample Parallax puts out, it very quickly burns out the PLL used to multiply the crystal input. Doh! In case anyone decides to try this thing, you absolutely must connect ALL ground and ALL power pins together externally with as short a connection as possible. Additionally, decoupling ceramic capacitors are all-but-required across the power pins as close to the chip as you can manage. Crap design if you ask me, especially without mentioning these needs in the documentation.

Thankfully, it'll still work at slower clock speeds or with an external clock source so I don't have to toss this one and find another chip, yet.
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09-29-2015, 06:02 PM,
#3
RE: Propeller P8X32A?
(09-28-2015, 01:02 AM)ABearden Wrote: Found the downside!

Ah bummer!

I've learned the need for decoupling caps the hard-way...I always put a .1uf cap across power and ground right at the chip now. Still, I'm surprised the grounds aren't all tied together internally.

Sorry to hear about the burn-out.

Was it a 4x PLL? So you're running at 20MHZ now?

I might have a 25MHZ resonator somewhere...that would speed you up a bit...but not back to 80MHZ where you were!
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09-29-2015, 07:13 PM,
#4
RE: Propeller P8X32A?
16x PLL with a 5MHz crystal. Further reading leads me to believe it corroded the internal bus for the PLL as it doesn't die until set to 8x. Someone on the forum theorized that the cross-chip power rail runs too close to the PLL and when the heat degrades the PLL connection it merely increases the resistance which is why it still works on the 4x and lower, but not at the 8x and 16x settings that require more power.

Yup, 20Mhz now which should still work; thanks for the offer though. There are examples of people doing video stuff with an Arduino at 16Mhz, I should be able to get by with 8 cores at 20Mhz. I'm seeing what I can do about an 80MHz external oscillator. Might get incorporated into the design even if I replace the chip so I'm not relying on an unreliable PLL design.
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09-30-2015, 07:07 AM,
#5
RE: Propeller P8X32A?
(09-29-2015, 07:13 PM)ABearden Wrote: ... it still works on the 4x and lower, but not at the 8x and 16x settings that require more power.

I took a (very) quick look at the data sheet...it seems to indicate the chip boots in 16x PLL mode, and THEN allows you to change the PLL settings? I couldn't get a read on what resonators / crystals are supported....I saw between 4 - 8 MHZ, but then saw settings for higher frequency resonators later on.

Anyway...I brought a 20MHZ resonator in...I'll drop it with Dan today at lunch (I'm attending a cross-country meet after work, so won't be at the create today...)

If it will work for you, feel free...center pin is ground...outside pins go to XTAL0 and XTAL1.

If you can still run 4x PLL, you should be back to full speed!

Brendan
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09-30-2015, 09:13 AM, (This post was last modified: 09-30-2015, 09:13 AM by ABearden.)
#6
RE: Propeller P8X32A?
Starts in RCSLOW on the internal oscillator, bumps up to RCFAST, then checks the bootloader for program-defined PLL/CLK settings to kick it into full speed. You can set the clock register at run-time as well. It'll accept anything from 4 to 60 MHz crystals, or a raw oscillator input (spec'ed to 80MHz, can hit 100MHz with chip propagation issues).

Thanks! I'll give it a try. I've been up since 3 going over NTSC specs and trying to figure out how to bit-bang a real-time video signal out w/o using the onboard generator. It's kinda daunting when you start measuring data output in the number of assembly commands you can execute per data burst. Won't turn down more cycles to utilize.
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09-30-2015, 11:37 PM,
#7
RE: Propeller P8X32A?
Thanks for the resonator!

Apparently the capacitance mismatch between the resonator and the PLL driver is causing it to run slow (at least, that's the only thing that makes sense to me for the results I'm seeing). At PLL4x it was only running 55MHz. However, it seems to be alright running the resonator at PLL8x and 110MHz. Mind you, I'm only running a serial-output loop on a single core so energy consumption is fairly low but I'm still confused why it'll run the resonator at 8x but not the crystal. Odd, but much faster than I was running!
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10-01-2015, 07:22 AM,
#8
RE: Propeller P8X32A?
(09-30-2015, 11:37 PM)ABearden Wrote: Thanks for the resonator!

Apparently the capacitance mismatch between the resonator and the PLL driver is causing it to run slow (at least, that's the only thing that makes sense to me for the results I'm seeing). At PLL4x it was only running 55MHz. However, it seems to be alright running the resonator at PLL8x and 110MHz. Mind you, I'm only running a serial-output loop on a single core so energy consumption is fairly low but I'm still confused why it'll run the resonator at 8x but not the crystal. Odd, but much faster than I was running!

Glad you're back in business!

My first computer was 1MHZ! I then went to an 8MHZ machine...woah!

Running at 110MHz, you're cooking with gas now! Enjoy!
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