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'DS1620 Digital Thermometer and Thermostat'
1997\10\22@203501 by Ken Pergola

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This should be an easy one...
 
Was hoping someone could verify something for me regarding the Dallas DS1620 Digital Thermometer/Thermostat.
 
When the DS1620 is in continuous conversion mode, polling the DONE bit for conversion status does not seem to be a good idea since it *seems* to be always logical 0 (conversion in progress). This makes sense why my PIC16C84 was caught in a loop waiting for the conversion to complete (logical 1). I'm not sure if the DS1620 always keeps the DONE bit cleared in this continuous mode *or* the chances of catching "1" in the DONE bit comes down to chance (due to the cyclical nature of continuous mode).
 
It *seems* that the DONE bit is only useful in one-shot mode (which I'm now using), but the data sheet does not particularly say so.
 
Any comments?
 
Please humble me if this seems obvious, but this may prevent someone else from wasting a few hours like I did.
 
Thanks,
 
Ken Pergola

1997\10\22@205125 by Steve Baldwin

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> When the DS1620 is in continuous conversion mode, polling the DONE bit
for conversion status does
> not seem to be a good idea since it *seems* to be always logical 0
(conversion in progress). This makes
> sense why my PIC16C84 was caught in a loop waiting for the conversion to
complete (logical 1).

> I'm not sure if the DS1620 always keeps the DONE bit cleared in this
continuous mode *or* the chances of
> catching "1" in the DONE bit comes down to chance (due to the cyclical
nature of continuous mode).
>
> It *seems* that the DONE bit is only useful in one-shot mode (which I'm
now using), but the data sheet
> does not particularly say so.
>
> Any comments?
>
> Please humble me if this seems obvious, but this may prevent someone else
from wasting a few hours like I did.

First comment is that your timing is impeccable. I just delivered a 1620
based device yesterday and did go through the time wasting.
There are a couple of things that aren't crystal clear in the data sheet. I
came to the same conclusion that you did regarding the done bit. The other
thing that wasn't very clear, was if the data register was buffered or not.
The diagram infers that it isn't but I was never able to get a stupid
reading, so it looks as though it is.
Random reading seems to be OK. I didn't try multiple reads within a (1
second) conversion time though.

Steve.

1997\10\22@231445 by Ken Pergola

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-----Original Message-----
From: Steve

>First comment is that your timing is impeccable. I just delivered a 1620
>based device yesterday and did go through the time wasting.
>There are a couple of things that aren't crystal clear in the data sheet. I
>came to the same conclusion that you did regarding the done bit. The other
>thing that wasn't very clear, was if the data register was buffered or not.
>The diagram infers that it isn't but I was never able to get a stupid
>reading, so it looks as though it is.
>Random reading seems to be OK. I didn't try multiple reads within a (1
>second) conversion time though.
>
>Steve.


Hi Steve,

Hey, thanks for your comments. I was a bit sheepish in posting the question,
but I'm glad I did. I think the DS1620 is a great device, but wish the data
sheet addressed some of these issues though. It appears that you will get
the last valid temperature reading while the DS1620 is busy.

I also remember talking to a Dallas rep a few years back when they were
having some problems with the DS1620 devices (latch-up or something). He
told me of an undocumented command. I'm not sure if it works, but command
0xAF was for resetting the device.

Thanks for your comments -- hopefully some more comments from others will
follow.


Ken Pergola

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