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Discussion Groups | 68HC12 | Re: HC12D60A sample capacitor / shared capacity?

Join our technical discussions about Freescale Microcontrollers: M68HC12. (Freescale Semiconductor is a Subsidiary of Motorola).

Re: HC12D60A sample capacitor / shared capacity? - James M. Knox - Apr 10 21:00:00 2003

At 11:22 AM 4/11/2003 +0200, you wrote:
>... yielding approx. 1.5pF,
>
>P.S.: I wish there were an extensive description of the ATD like in
>the Pink Book.

Amen, brother. For the HC12 there isn't even a good description of the
input impedance to a working ATD. Somewhere between 10K and 20K,
apparently, but nothing well defined.

1.5 pf seems VERY low - much too low for a sanple&hold. But I admit I
haven't tried to measure it directly.

[Heck, I'm still trying to figure out why I've got identical boards with
VASTLY different ATD noise levels!!!]

jmk -----------------------------------------------
James M. Knox
TriSoft ph 512-385-0316
1109-A Shady Lane fax 512-366-4331
Austin, Tx 78721
-----------------------------------------------




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Re: HC12D60A sample capacitor / shared capacity? - James M. Knox - Apr 11 4:06:00 2003

At 01:01 PM 4/11/2003 -0700, you wrote:
>Could the noise be INTERNAL to the MCU?

That's what I am suspecting. But why is there so MUCH difference between
the MCU's? With one exception, every board we have falls VERY CLEARLY into
one of two pigeon holes. It's not that we have a broad spectrum of noise,
it's that it is either fairly noisy or VERY clean!

>As an experiment, could you tinker the code on one of the bad boards to try
>reading the ADC after 10 to 100 us or no other I/O activity?

On the test jig I can pretty much set things up so that the only I/O
activity is just the writes out the SCI port. Doesn't seem to make much
difference.

>Is there any sign of noise on the power or ground pins of the MCU?

Very little. Perhaps more importantly, I see *NO* difference between the
noise on the "clean" boards and the noise on the "noisy" boards.

The one thing I haven't tried, because of the difficulty, is actually
trying to pull (without harming them) one D60A from a "quiet" board and one
from a "noisy" board and swapping them. That would be a big pain, but the
only way to really tell if it is in the processor or not.

jmk -----------------------------------------------
James M. Knox
TriSoft ph 512-385-0316
1109-A Shady Lane fax 512-366-4331
Austin, Tx 78721
-----------------------------------------------




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HC12D60A sample capacitor / shared capacity? - Oliver Betz - Apr 11 4:22:00 2003

Hello All,

the HC12 ATD connects a "sample capacitor" to the input node for 2
ATD cycles, this capacitor stays charged until the next conversion
and has then to be charged to the new voltage by the source.

I find no specs about the (max.) value of this shared capacity in the
"Technical Data" but I believe that there was some FAQ, EB or so. Any
hint where to look?

"Technical Data" specifies "max. input capacitance non sampling" 10pF
and "sampling" 15pF, but this doesn't tell much about the max. value
of the shared capacity, since the "non sampling" capacity could be
less then 10pF...

I did my own experiments extrapolating the different deviations at
various "final sampling time" settings, input resistances and
parallel capacitances, yielding approx. 1.5pF, but a confirmation
would be nice.

Oliver

P.S.: I wish there were an extensive description of the ATD like in
the Pink Book.
--
Oliver Betz, Muenchen




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Re: HC12D60A sample capacitor / shared capacity? - Oliver Betz - Apr 11 10:08:00 2003

James M. Knox wrote:

> >... yielding approx. 1.5pF,
> >
> >P.S.: I wish there were an extensive description of the ATD like in
> >the Pink Book.
>
> Amen, brother. For the HC12 there isn't even a good description of the
> input impedance to a working ATD. Somewhere between 10K and 20K,
> apparently, but nothing well defined.

The input impedance is _much_ higher. I already had 220kOhms source
impedance with only FS 1% error (16 cycles final sampling time). And
the shared capacitance behaves like several MOhms between successive
channels even when converting with max. speed.

> 1.5 pf seems VERY low - much too low for a sanple&hold. But I admit I
> haven't tried to measure it directly.

It's not a real sample and hold but a shared input capacitance of a
multiplexer and an amplifier (I guess). The HC11 has no amplifier and
therefore the pin is connected directly to the ATD capacitor (array).

> [Heck, I'm still trying to figure out why I've got identical boards with
> VASTLY different ATD noise levels!!!]

I have several boards (812A4, 912D60A) with not even separate ATD
supply decoupling, and always got less than 1 count noise (8 bit
resolution) with 2 or four cycles final sampling.

Oliver
--
Oliver Betz, Muenchen




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Re: HC12D60A sample capacitor / shared capacity? - James M. Knox - Apr 11 12:51:00 2003

At 05:08 PM 4/11/2003 +0200, you wrote:

>I have several boards (812A4, 912D60A) with not even separate ATD
>supply decoupling, and always got less than 1 count noise (8 bit
>resolution) with 2 or four cycles final sampling.

What I have is just plain strange. A run of 10 boards, all built up at the
same time, from the same parts. On three boards I get 10 bits, +/-
LSB. Beautiful!!!

On six boards I get at least twice the noise, no better than 9 bits, and
probably more like 8 bits.

One one board, I don't even get that... same type of noise, but cost me at
least down to 7 bits. [All these boards were run on the exact same test
bench.]

With a scope I see NO difference between ANY of the boards. What little
noise I do see, I see on all the boards.

I'm just about down to the thought that maybe it varies by mask or date
code of the D60A itself. [The D60A's were overruns from another company's
project, and *may* or *may not* include various date/mask
codes.] Unfortunately, the board cleanup process seems to have done an
excellent job of removing any trace of the printing on the top of the IC,
so that history is lost.

Very strange.
jmk -----------------------------------------------
James M. Knox
TriSoft ph 512-385-0316
1109-A Shady Lane fax 512-366-4331
Austin, Tx 78721
-----------------------------------------------




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Re: HC12D60A sample capacitor / shared capacity? - Steve Russell - Apr 11 15:01:00 2003

Could the noise be INTERNAL to the MCU?

As an experiment, could you tinker the code on one of the bad boards to try
reading the ADC after 10 to 100 us or no other I/O activity?

Is there any sign of noise on the power or ground pins of the MCU?

Steve

At 10:51 AM 4/11/2003, you wrote:
>At 05:08 PM 4/11/2003 +0200, you wrote:
>
> >I have several boards (812A4, 912D60A) with not even separate ATD
> >supply decoupling, and always got less than 1 count noise (8 bit
> >resolution) with 2 or four cycles final sampling.
>
>What I have is just plain strange. A run of 10 boards, all built up at the
>same time, from the same parts. On three boards I get 10 bits, +/-
>LSB. Beautiful!!!
>
>On six boards I get at least twice the noise, no better than 9 bits, and
>probably more like 8 bits.
>
>One one board, I don't even get that... same type of noise, but cost me at
>least down to 7 bits. [All these boards were run on the exact same test
>bench.]
>
>With a scope I see NO difference between ANY of the boards. What little
>noise I do see, I see on all the boards.
>
>I'm just about down to the thought that maybe it varies by mask or date
>code of the D60A itself. [The D60A's were overruns from another company's
>project, and *may* or *may not* include various date/mask
>codes.] Unfortunately, the board cleanup process seems to have done an
>excellent job of removing any trace of the printing on the top of the IC,
>so that history is lost.
>
>Very strange.
> jmk >-----------------------------------------------
>James M. Knox
>TriSoft ph 512-385-0316
>1109-A Shady Lane fax 512-366-4331
>Austin, Tx 78721
>----------------------------------------------- >Yahoo! Groups Sponsor
><http://us.ard.yahoo.com/M=249982.3083889.4452939.1728375/D=egroupweb/S=1706554205:HM/A=1524963/R=0/*http://hits.411web.com/cgi-bin/autoredir?camp=556&lineid=3083889&prop=egroupweb&pos=HM>5038ad.jpg
>
>503957.jpg
>
>--------------------------------------------------------
>To unsubscribe from this group, send an email to: >To learn more about Motorola Microcontrollers, please visit
><http://www.motorola.com/mcu>http://www.motorola.com/mcu >>Yahoo! Terms of Service. *************************************************************************
Steve Russell mailto:
Senior Software Design Engineer http://www.nohau.com
Nohau Corporation phone: (408)866-1820
51 East Campbell Avenue fax: (408)378-7869
Campbell, CA 95008
*************************************************************************

[Non-text portions of this message have been removed]




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RE: HC12D60A sample capacitor / shared capacity? - Kellogg Dave - Apr 11 16:03:00 2003

Does the 'D60A have a mode in the A/D where you can read an internal
voltage, such as Vrh/2? That might cast some light on the situation. 607-656-2597 -----Original Message-----
From: Steve Russell [mailto:]
Sent: Friday, April 11, 2003 4:02 PM
To:
Subject: Re: [68HC12] HC12D60A sample capacitor / shared capacity? Could the noise be INTERNAL to the MCU?

As an experiment, could you tinker the code on one of the bad boards to try
reading the ADC after 10 to 100 us or no other I/O activity?

Is there any sign of noise on the power or ground pins of the MCU?

Steve

At 10:51 AM 4/11/2003, you wrote:
>At 05:08 PM 4/11/2003 +0200, you wrote:
>
> >I have several boards (812A4, 912D60A) with not even separate ATD
> >supply decoupling, and always got less than 1 count noise (8 bit
> >resolution) with 2 or four cycles final sampling.
>
>What I have is just plain strange. A run of 10 boards, all built up at
>the same time, from the same parts. On three boards I get 10 bits, +/-
>LSB. Beautiful!!!
>
>On six boards I get at least twice the noise, no better than 9 bits,
>and probably more like 8 bits.
>
>One one board, I don't even get that... same type of noise, but cost me
>at least down to 7 bits. [All these boards were run on the exact same
>test bench.]
>
>With a scope I see NO difference between ANY of the boards. What
>little noise I do see, I see on all the boards.
>
>I'm just about down to the thought that maybe it varies by mask or date
>code of the D60A itself. [The D60A's were overruns from another
>company's project, and *may* or *may not* include various date/mask
>codes.] Unfortunately, the board cleanup process seems to have done an
>excellent job of removing any trace of the printing on the top of the
>IC, so that history is lost.
>
>Very strange.
> jmk >-----------------------------------------------
>James M. Knox
>TriSoft ph 512-385-0316
>1109-A Shady Lane fax 512-366-4331
>Austin, Tx 78721
>----------------------------------------------- >Yahoo! Groups Sponsor
><http://us.ard.yahoo.com/M=249982.3083889.4452939.1728375/D=egroupweb/S
>=1706554205:HM/A=1524963/R=0/*http://hits.411web.com/cgi-bin/autoredir?
>camp=556&lineid=3083889&prop=egroupweb&pos=HM>5038ad.jpg
>
>503957.jpg
>
>--------------------------------------------------------
>To unsubscribe from this group, send an email to: >To learn more about Motorola Microcontrollers, please visit
><http://www.motorola.com/mcu>http://www.motorola.com/mcu >>Yahoo! Terms of Service. *************************************************************************
Steve Russell mailto:
Senior Software Design Engineer http://www.nohau.com
Nohau Corporation phone: (408)866-1820
51 East Campbell Avenue fax: (408)378-7869
Campbell, CA 95008
*************************************************************************

[Non-text portions of this message have been removed]
--------------------------------------------------------
To unsubscribe from this group, send an email to: To learn more about Motorola Microcontrollers, please visit
http://www.motorola.com/mcu



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RE: HC12D60A sample capacitor / shared capacity? - Darren - Apr 11 21:20:00 2003

James,

You could look at the errata for all the masks for
the D60, and test to see which bugs are in the chips
you have, you should then be able to work out which
masks you have on your boards....

Darren Moore

> -----Original Message-----
> From: James M. Knox [mailto:]
>
> At 05:08 PM 4/11/2003 +0200, you wrote:
>
> >I have several boards (812A4, 912D60A) with not even separate ATD
> >supply decoupling, and always got less than 1 count noise (8 bit
> >resolution) with 2 or four cycles final sampling.
>
> What I have is just plain strange. A run of 10 boards, all
> built up at the
> same time, from the same parts. On three boards I get 10 bits, +/-
> LSB. Beautiful!!!
>
> On six boards I get at least twice the noise, no better than
> 9 bits, and
> probably more like 8 bits.
>
> One one board, I don't even get that... same type of noise,
> but cost me at
> least down to 7 bits. [All these boards were run on the
> exact same test
> bench.]
>
> With a scope I see NO difference between ANY of the boards.
> What little
> noise I do see, I see on all the boards.
>
> I'm just about down to the thought that maybe it varies by
> mask or date
> code of the D60A itself. [The D60A's were overruns from
> another company's
> project, and *may* or *may not* include various date/mask
> codes.] Unfortunately, the board cleanup process seems to
> have done an
> excellent job of removing any trace of the printing on the
> top of the IC,
> so that history is lost.
>
> Very strange.
> jmk > -----------------------------------------------
> James M. Knox
> TriSoft ph 512-385-0316
> 1109-A Shady Lane fax 512-366-4331
> Austin, Tx 78721
> -----------------------------------------------



(You need to be a member of 68hc12 -- send a blank email to 68hc12-subscribe@yahoogroups.com )

Re: HC12D60A sample capacitor / shared capacity? - Steve Russell - Apr 11 21:53:00 2003

Well, here's another thought.

There could be some storage and assembly process problems.

I have some war stories...

Rather than un soldering one of your "good" boards, get a new good chip,
and replace the one on your worst board.

If the problem goes away, you have a simple fix.

Both of the problems in my war stories get worse with time.

The war stories (short form)...

A long time ago in a land far far away (Maynard, Mass.) a fledgling
computer manufacturer made some boards with tinned copper bus wire that
turned out to have been left outside in New England weather for too long.

The solder joints that connected this wire to the circuit boards looked
like good solder joints, and the boards passed their tests.

After 6 to 18 months the solder joints gradually corroded enough to become
lead oxide diodes of doubtful but variable properties. Many intermittents
and much agony resulted.

This year a local company that I have contact with has been having problems
with some of new BGA packages. (Not from Motorola.) Careful inspection
showed that the packages had separated.

The result of the cracks was variously to just plain not work, or to not
work after a while.

The problem here was that their PCB assembly group was not carefully
following the instructions about keeping the packages in a dry atmosphere
or baking them for 24 hours before assembly if they had been removed from
their sealed shipping packages.

The packages that HC-12s come in have similar instructions.

In our lab we don't always follow the instructions with HC-12 parts, and we
don't often get in trouble for it, but if you packages are compromised,
excess noise in the analog circuits would not be surprising.

Steve

At 02:06 AM 4/11/2003, you wrote:
>At 01:01 PM 4/11/2003 -0700, you wrote:
> >Could the noise be INTERNAL to the MCU?
>
>That's what I am suspecting. But why is there so MUCH difference between
>the MCU's? With one exception, every board we have falls VERY CLEARLY into
>one of two pigeon holes. It's not that we have a broad spectrum of noise,
>it's that it is either fairly noisy or VERY clean!
>
> >As an experiment, could you tinker the code on one of the bad boards to try
> >reading the ADC after 10 to 100 us or no other I/O activity?
>
>On the test jig I can pretty much set things up so that the only I/O
>activity is just the writes out the SCI port. Doesn't seem to make much
>difference.
>
> >Is there any sign of noise on the power or ground pins of the MCU?
>
>Very little. Perhaps more importantly, I see *NO* difference between the
>noise on the "clean" boards and the noise on the "noisy" boards.
>
>The one thing I haven't tried, because of the difficulty, is actually
>trying to pull (without harming them) one D60A from a "quiet" board and one
>from a "noisy" board and swapping them. That would be a big pain, but the
>only way to really tell if it is in the processor or not.
>
> jmk >-----------------------------------------------
>James M. Knox
>TriSoft ph 512-385-0316
>1109-A Shady Lane fax 512-366-4331
>Austin, Tx 78721
>----------------------------------------------- >Yahoo! Groups Sponsor
>ADVERTISEMENT
><http://rd.yahoo.com/M=246920.2960106.4328965.1728375/D=egroupweb/S=1706554205:HM/A=1513703/R=0/*http://www.gotomypc.com/u/tr/yh/cpm/grp/300_06F/g22lp?Target=mm/g22lp.tmpl>1c976c7.jpg
>
>1c97735.jpg
>
>--------------------------------------------------------
>To unsubscribe from this group, send an email to: >To learn more about Motorola Microcontrollers, please visit
><http://www.motorola.com/mcu>http://www.motorola.com/mcu >>Yahoo! Terms of Service. *************************************************************************
Steve Russell mailto:
Senior Software Design Engineer http://www.nohau.com
Nohau Corporation phone: (408)866-1820
51 East Campbell Avenue fax: (408)378-7869
Campbell, CA 95008
*************************************************************************

[Non-text portions of this message have been removed]



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Re: HC12D60A sample capacitor / shared capacity? - Oliver Betz - Apr 12 6:04:00 2003

James M. Knox wrote:

[Noisy A/D-conversions on some boards]

[...]

> >Is there any sign of noise on the power or ground pins of the MCU?
>
> Very little. Perhaps more importantly, I see *NO* difference between the
> noise on the "clean" boards and the noise on the "noisy" boards.

How did you measure the power supply noise? You need at least 100MHz
scope bandwidth and very short connections to the board, e.g. thin
coax cable directly soldered to GND/VCC and 50Ohms terminated at the
scope side.

Are there different supply voltages? If you let the clamping diodes
of one ADC channel conduct, this will influence other channels of the
ADC. This effect isn't described for the HC12D60 but for the 9S12
derivatives (even quantitative).

Checked all solder joints? Sure that the ADC supply voltage is
connected?

Oliver
--
Oliver Betz, Muenchen



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