Mimic SAA1043 to generate PAL CCIR sync

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Hello all, anyone with video experience or specifically SAA1043 sync generator? I have a circuit and want to replace SAA1043 with atmega. In this circuit SAA1043 is locking an external sync signal and generating a burst flag and composite sync, schematics attaching below. For this I need some help in understanding what exactly these two signals mean and how do I formulate the output with Atmega controller.

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Last Edited: Sun. Mar 10, 2019 - 11:11 AM
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sidk wrote:

...anyone with video experience or specifically SAA1043 sync generator?...

 

You called? I have both.

 

The SAA1043 is doing a number of functions here...

 

1) It takes in composite sync and separates out line sync.

2) It feeds that, along with the line sync it is generating to a phase comparator.

3) The phase comparator drives a VCO (voltage controlled oscillator).

4) The oscillator drives the timing generator to generate all the signals, including the line sync signal used in 1).

 

 

4) is very easy to do with an AVR and can be done very accurately. The other parts are either very difficult to do or impossible to do with an AVR. Certainly there is no way to make a VCO with software inside the AVR.

 

Is this for a production unit or you just need to replace one SAA1043?

 

 

#1 This forum helps those that help themselves

#2 All grounds are not created equal

#3 How have you proved that your chip is running at xxMHz?

#4 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand." - Heater's ex-boss

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Thanks for your attention. As per task in hand I need to replace 3 cards max.

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Brian Fairchild wrote:

 

The other parts are either very difficult to do or impossible to do with an AVR. Certainly there is no way to make a VCO with software inside the AVR

 


So what do you suggest? Any other IC which can perform this function? Because SAA1043 is obsolete now and I want to use something easily available.
Please suggest. Thanks

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sidk wrote:
Thanks for your attention. As per task in hand I need to replace 3 cards max.

 

I would go onto eBay and buy three SAA1043s. There are some for sale right now.

 

The alternative is going to be something like a 3 chip, plus lots of passives, solution...

 

Sync Separator .... Texas LM1881 or something from Elantec (now Renesas)

VCO running at 10Mhz minimum, better at 20Mhz, something like an HCxx46

 

....plus the AVR.

#1 This forum helps those that help themselves

#2 All grounds are not created equal

#3 How have you proved that your chip is running at xxMHz?

#4 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand." - Heater's ex-boss

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And to program AVR do you have some article or paper for reference from where I can get to study how these sync signals work?

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Without knowing exactly what the rest of the circuit is doing it's difficult to know if this will work but have a look at the datasheet for the EL4583. It *might*, on its own, do what you need.

#1 This forum helps those that help themselves

#2 All grounds are not created equal

#3 How have you proved that your chip is running at xxMHz?

#4 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand." - Heater's ex-boss

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/me sings - Anything a PIC can do an AVR can do better, An AVR can do anything better than PIC

 

As Brian said there is no way to make a VCO with software inside an AVR.

 

You can however use a GPIO (PWM or DAC) to change the capacitance of a varactor (or any signal diode really) that is on one leg of the XTAL osc.

 

You now have a VCO.  You can use an input capture to get the timing syncs in and use some fancy software to control the VCO and use an OC to make the syncs out.

 

All the functions you need with the addition of a couple of cents worth of passives.

 

If you are super keen you can even use OSC_CAL to make the internal oscillator work as a VCO.  I never got that to work reliably 100% of the time though so I don't recommend it.

 

I don't know if you already have the incoming syncs DC coupled.  If so the Input Capture can just be run from the analog comparator with nothing fancy.  If the incoming video does not have a known DC reference you will have to use an edge detector on the analog comparator.

 

(Look up "SSAVI 3Chip" if you want to know what my musical outburst at the start was about)

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sidk wrote:
And to program AVR do you have some article or paper for reference from where I can get to study how these sync signals work?

 

Any good reference on the PAL composite signal will tell you all there is to know on how a video signal works. As to doing it in an AVR, sorry I've never come across anything. All my work has been from first principles and a lot of trial and error.

#1 This forum helps those that help themselves

#2 All grounds are not created equal

#3 How have you proved that your chip is running at xxMHz?

#4 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand." - Heater's ex-boss

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Brian Fairchild wrote:

Without knowing exactly what the rest of the circuit is doing it's difficult to know if this will work.

Rest is sync amplification. Attaching it

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For completeness.  Here is a PCB that takes an AC coupled composite signal.  It uses an edge detector on the analog comparator pin.  Software then searches for "combs" in VSync.  There is some smart time based filtering to avoid false positives from rapid brightness changes in active video.  It then "gates" in software  its search for VSyncs.  It uses the time of arrival of these syncs to alter the DC value on the top of the signal diode that makes the XTAL OSC into a VCO.

 

You can see that the chip is an AT90S2313 not an ATTiny.  So that should give you an idea of the vintage (or maybe the date code 99 is a better indicator).

 

The production version switched to a real varactor and also had a tuning cap to get the xtal close to 10/20Mhz so it had more "pull range"

 

 

Sync Syncer with an AVR

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Brian Fairchild wrote:

It *might*, on its own, do what you need.


So after looking at complete schematics do you think EL4583 will work? To me it seems that it generates both wanted signals.

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So after looking at complete schematics do you think EL4583 will work? To me it seems that it generates both wanted signals.

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sidk wrote:
So after looking at complete schematics do you think EL4583 will work? To me it seems that it generates both wanted signals.

 

That's what prototypes are for.

#1 This forum helps those that help themselves

#2 All grounds are not created equal

#3 How have you proved that your chip is running at xxMHz?

#4 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand." - Heater's ex-boss

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Thank you so much for the kind suggestions, you guys are really helpful.