Multiple Prop Design

steprog

Hello,
Im working up a dual prop design and I was wondering how can you sync up the clocks for both props.· Do you use one end of the crystal to feed the other prop?· I looked at the six bladed prop schematic and it seems that individual crystals are used.· Any ideals?
·

Bill Henning

Originally I used one Prop with a crystal to generate a 5MHz clock for the second prop using a counter, but I had problems generating video on the (counter driven) prop.

Now I use separate crystals.

If I wanted to have two props in exact sync, I'd use a 74HC04 to excite the crystal, and feed the output from a buffer to XIN on both props.

steprog said...
Hello,
Im working up a dual prop design and I was wondering how can you sync up the clocks for both props. Do you use one end of the crystal to feed the other prop? I looked at the six bladed prop schematic and it seems that individual crystals are used. Any ideals?

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steprog

Sounds good, but I was hoping to reduce part count.

Mike Green

Every solution has a down side. You cannot use the clock oscillator on a Prop to feed anything else.

1) Each Prop has its own crystal / You need a crystal for each and they're not really synced

2) Use a 74HC04 or equivalent to make a crystal oscillator, buffer the output using two gates of the 74HC04 and feed each gate to a Prop / This needs a 74HC04

3) Use a counter on one Prop to generate the clock for another Prop / Every program has to enable the counter on one cog and it uses an I/O pin for the clock output

steprog

Thanks Mike, I may give option 3 a shot

Cluso99

3 alternatives and here is the 4th...
4. Use a chip oscillator.

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· Prop Tools under Development or Completed (Index)
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kuroneko

steprog said...
Thanks Mike, I may give option 3 a shot

Unwanted(?) side effect: when you reset the clock provider prop, the receiver prop hangs when it's using PLL clock generation.

jmg

Or, use a 3 Gate HCU04 device : comes in SO8 so is easy to handle, and the U04 is needed for Oscillator design.
Or, use a more specific, and smaller device like the 1GX04 - that has high drive and can feed multiple targets

ErNa

Try this: one prop uses a crystal, and connect XO to the other props XIn s. The secondatry props will see the input signals as the feedback of the crystal and will "oscillate" at 5 MHz. Don't tell the slave props about that!

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Sapieha

Hi ErNa.

Yes - Some oscillator's CAN run that way BUT in that connection them have/need one CAPacitor connected between XO (in first IC) and XI of next stage(IC).

But I not have tested Propeller YET if that's connection works on Propeller.

Regards

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Sapieha

Ariba

Since I've seen the FullSpeed USB Host thread, I believe no longer if someone just says: it is not possible or it does not work.

So I just tried to connect 2 Propellers on 2 Boards with 200mm Cable between XO of the first Prop to XI on the second Prop.
I removed the crystal on the second Board (a ProtoBoard) and started two time the same program with TV output.

Works with no problems, I get a stable TV picture from both Boards. Crystal on Board 1 is 5 MHz, both uses PLLx16.
I can set the first crystal mode to XTAL1 or XTAL2 -> both works.
I can set the second Prop without crystal to XTAL1, XTAL2, or XTAL3, all works.
I can use a serial 1nF capacitor between XO_1 and XI_2, or a direct connection -> it works.

From the values in the datasheet I would recommend XTAL3 for the second Prop because this gives the lowest pin capacity.

Andy

Sapieha

Hi Ariba.

Thanks for tests.

But I still recommend Series capacitor.

Regards

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Nothing is impossible, there are only different degrees of difficulty.
For every stupid question there is at least one intelligent answer.
Don't guess - ask instead.
If you don't ask you won't know.
If your gonna construct something, make it·as simple as·possible yet as versatile as posible.


Sapieha

Ariba

Saphiea

I think if the voltage swing would be so low, that the the input Threshold level is a problem, then you need also a feedback resistor between XO and XI of the slave Prop (1 MOhm or so). With only a capacitor the DC level at the XI is unknown.
But the swing seems to be high enough and the threshold level matches good enough.

Andy

Sapieha

Hi Ariba.

If You have very good Oscilloscope and measure ON XI pin that is driven by XTal - You will see that XI on it have very small Voltage swings to function correctly
Adding series capacitor have no impact for functioning on XI-2 but very big impact on XO-1 (protect for DC voltages to be feed back to XO-1 that can burn it)
as XI-2 need as said very small voltage swings to function.

Regards

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Nothing is impossible, there are only different degrees of difficulty.
For every stupid question there is at least one intelligent answer.
Don't guess - ask instead.
If you don't ask you won't know.
If your gonna construct something, make it·as simple as·possible yet as versatile as posible.


Sapieha

Harley

I am using a two-Prop board interfaced with a bunch of TTL ICs. Prop#1 uses a 5 MHz crystal and uses A24 to output a 5 MHz square wave signal using CTRB in NCO mode to Prop#2 X1 input. Communications between the two Props is via FullDuplexSerial object at 115,200 baud. No problems have been observed with this setup.

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Harley Shanko

dr hydra

Mike,

Can you post a schematic for option #2...I am not sure what that would look like

dr hydra

2) Use a 74HC04 or equivalent to make a crystal oscillator, buffer the output using two gates of the 74HC04 and feed each gate to a Prop / This needs a 74HC04

What would this look like (any schematics or drawings)...I cannot picture this