68300

Prashant,
 
I tried to call you today (8:30 am in Austin, Texas, USA).  I don't think I dialed the number right.  Do I need a country code or is "91" the country code.  You can sure tell I don't dial many international numbers.
 
Any way, I do not believe that your problem is too serious.
 
First of all, I need a little information from you.
 
You stated in your email that everything was working but now, with the new production, things are NOT working.  Now, look at one of the 68332's from the "old" production and one from the "new" production.  I suspect that these parts will be different mask sets.  The newest mask set is J30C. I suspect that these will be the parts that are giving you trouble.  (Earlier mask sets include J66A and F98R)  You can determine the mask number by reading the markings on the package.  The mask set number is right under the Part Number.
 
Anyway, J30C does not have quite as much drive capability as prior mask sets.  This has more to do with the wafer line than the mask set but J30C is only made in one wafer line.  In fact, mask sets are tied to specific wafer lines.
 
So, there are several things to look at.
 
1.  Do you have the "X" bit in the SYNCR register set to a logic 1?  This controls the "divide by 2" circuit on the output of the internal PLL / VCO.  If it is NOT a logic 1, change it to a logic 1 and then adjust the "Y" bits to get the proper frequency.  In other words, if you are operating the 68332 system clock above 8 MHz,  then look at the table in the 68332 manual where it gives divider ratios to obtain various system frequencies based on the X, W and Y bits.  Choose a value from the right hand column.  That is, make sure to use a value with X = 1.
 
2.  Next, it is critical that you use the 3-component (High Stability XFC filter).  If you are not using the High Stability Filter your circuit is going to have clock jitter in the PLL/VCO.  The Normal Stability XFC filter is a singel 0.1 uf capacitor from the XFC pin to Vddsyn.  The 3 component filter is an 18 Kohm resistor in series with a 0.1 uf cap between XFC and Vddsyn.  In parallel with these two components is a 0.01 uf cap.
 
3.  Third, you want to see if your crystal is starting correctly.  The best way to do this is take a scope and monitor CLKOUT.  (DO NOT monitor XTAL or EXTAL  --  the scope will load these pins and give you crazy readings.)
 
Since the J30C mask set does not have quite as much drive capability as prior mask sets, you might have to reduce the value (less ohms) of the series resistor in the external crystal circuit.  Many times, the series resistor is around 330 Kohm.  This may be too big (too many ohms).  There should be about a 200 to 400 millisecond delay between the application of power to the appearance of an 8.3 MHz signal on CLKOUT. If the series resistor is too small (less ohms) the 68332 may be overdriving the crystal and give really strange start up characteristics.  If the series resistor is too big, the crystal will take a very long time to start.
 
Anyway, check these things out and let me know your results.  Be sure to check the mask sets.  J30C is the only mask set in production and it will be the only one in production for a very long time into the future.  So, you need to take into account the requirements of this mask set.  That is, use the 3-component XFC filter, make sure the X bit = 1 and properly size the series resistor in the external crystal circuit.
 
Best regards,
 
 
Charlie
 

-----Original Message-----
From: development [mailto:development@...]
Sent: Thursday, May 08, 2003 2:24 AM
To: 68300@yahoogroups.com
Subject: [68300] PLL not locking/ erratic xtal behavior


Hi All, 
    I am facing a very peculiar problem. I am working on 
68332 with a 32.768 kHz xtal. The design was working fine 
in all the boards previously, but lately the xtal seems to 
going haywire.

    The only difference is that I have now a new set of 
boards, without any change in the crystal circuit. The PLL 
circuit does not lock by itself but if I place my finger 
somewhere near the xtal, it locks. 

It will run like that for some time but then it starts 
behaving erratically. 

   I am using two 22pF capacitors along with a 330K resitor 
and the feedback resistor value is 10M. On the xtal it is 
written KDS 32.768.

Any suggestions

Regards,
Prashant Alange
R&D Department,
ID Technologies. (A division of mark elektriks)
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Oppo. Corporation Bank,  | TeleFax: +91-20-5410479
Maharshi Karvenagar,     | Email: development@...
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Pune - 411052. India.    |
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