'Do you know 14000?'
I'm going to work on 14000 pic family.
Advises are welcome.
I've been playing with one for a week or so and the A - D
seems to be tricky.
I don't know if it's due to drift in the capacitor value,
or noise or what, but I can't get more than 10 - 12 bits
of accuracy ( *not* resolution ) out of it. The last 4 bits
are just pure jitter.
Otherwise, it is just another PIC
. Never trust a man who, when left alone in ....... Pete Lynch .
. a room with a tea cosy, doesn't try it on ....... Marlow, England .
..........Billy Connolly. ......................... beowulf.demon.co.uk .. pic
On Sat, 21 Nov 1998 AOL.COM wrote: Spk41q
> I'm going to work on 14000 pic family.
> Advises are welcome.
|Yes...my first PIC... :-/
First: Read the errata sheet !
(Strange the main data sheet is still "preliminary"!?)
Problems i«ve found not documented in the errata sheet:
1) Upgrade your picstart + to version 7 or later, (lower VPP)
Before i did, my PIC14000JW date code 9752SAT got their code protect bit
set to "illegal" as it reports (whatever that mean) even if i selected not
to program it! I also upgraded to firmware 1.50.00, that might have
(I described the procedure in a posing recently)
2) Date code 9650SAT seem to program correct with elder picstart +, but if
you select HS mode the A/D still keep running on 4MHz internal osc, while
CPU runs at external! (...or if it was the other way around, real fuzzy
anyway, drove me crazy for a while)
Know, that this is a very cheap single ramp converter.
It needs to be calibrated often against the internal refs, and mchip have
already programmed the calibration data into *EPROM*.
First thing to do when you get the chips is to mark them with different
numbers and read out the calibration data and save it, before you erase them!
Also check how your code handle A/D overflow, and test close-to overflow.
I«m currently trying to figure out why it sometimes wrap..!?
And use good noise filtering!
Except the above it seem to work as expected.
Carefully select what pin you want to do what, as they are physically very
different; D/A with or without ofset or sum cap, I2C pins with different
drive, D/A ref outputs, compare inputs, etc...
Also the strange D/A converters for onboard comparators have a really weird
construction which also has a S-shape conversion curve, not starting from
zero volts, etc. Apparently a custom chip from beginning.
(I have made a conversion routine from linear binary to PIC14000 D/A, if
somebody is interested to share code.)
Well, the chip is pretty cheap if we can use all functions, and RAM and ROM
are amongst the largest for a PIC16xx.
And do anybody know what the following mean;
this text i have found as note in the demo code:
"...there is a possibility that the timer count is captured very shortly
after overflow occurs, resulting in erroneous a/d reading. see application
note for more details. "
How "very shortly", what (might?)happen, what appnote, where???
Please somebody tell!
Morgan Olsson ph +46(0)414 70741
MORGANS REGLERTEKNIK fax +46(0)414 70331
H€LLEKS (in A-Z letters: "HALLEKAS")
SE-277 35 KIVIK, SWEDEN iname.commrt
'Do you know 14000?'
|Know, that this is a very cheap single ramp converter.
|It needs to be calibrated often against the internal refs, and mchip have
|already programmed the calibration data into *EPROM*.
One problem with the ramp converter on the PIC14000's from what
I've heard is that like all latched-count single-ramp convertors
it is extremely sensitive to input noise. A brief glitch on the
input may cause the A/D to latch its count prematurely. An alt-
ernative A/D technique which I've used with good success is app-
licable to any PIC with the addition of a simple comparator chip,
a resistor, and a cap. [Details of technique discussed in other
emails before]. While my technique is a bit slow to respond to
rapidly changing signals, it has excellent noise immunity and its
accuracy is dependent only upon the following factors:
 Offset errors or (to a much smaller extent) delayed response
in the comparator.
 The stability of the PIC's "high" and "low" output levels. If
these levels are unstable (e.g. because the PIC is driving high-
current I/O devices) an external chip with good 5.0 and 0.0 volt
outputs may be used.
Note that the device does not put any significant load on the PIC
port output that it uses, nor does it depend upon the accuracy of
R and C (a smaller RC will result in faster readings but add some
"random" error to the readings) The one drawback is the necessity
of a uniform periodic service routine.
Has anyone else used my A/D method? Any results good/bad?
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