Re: [oopic] Re: DDELink bug and linking 2 Oopic Rs

One other thing - The problem does not exist when using ooPIC II+ chips,
ooPIC II or any other ooPIC version on ooPIC S boards. It ONLY happens
when using an ooPIC R or ooPIC C, which use the QFP packages, and are
16F877a chips.

DLC

dan michaels wrote:
> --- In oopic@yahoogroups.com, ooPIC Tech Support <dennis.clark@...>
> wrote:
>
>>I've played with this problem for off and on for a while it seems
>
> and
>
>>can't find any good explanation or reasoning. You should be using
>
> 2.7K
>
>>to 4.7K for even short distances (measured in single digit
>
> centimeters)
>
>>but it simply won't work between any two ooPICs that use the
>
> 16F877a
>
>>processor and I just don't understand why.
>
>
>
>
> I've never played with DDE, but this large resistor value business
> makes no sense, as the 877(A) pins can all source and sink upwards to
> 20-mA. 5v/20mA = 250 ohms!
>
> I wonder if there isn't some problem with the code on the newer
> firmware not switching modes properly between output and input, ie
> some timing issue, when the data transfers switch direction.
>
> JFTHOI, you might try putting a small series R in the leads between
> the 2 OOPic 2+ chips and see if that helps. Just a shot in the dark.
>
>
>
>
> Putting an ooPIC S board in
>
>>the circuit fixes it, so that left out cable length, noise in the
>
> wires
>
>>or just bad connectors. If anyone can figure out why this happens
>
> I
>
>>offer up a 4 pack of Guiness Draught cans as a prize!
>>
>>DLC
>>
>>rtstofer wrote:
>>
>>>--- In oopic@yahoogroups.com, ooPIC Tech Support <dennis.clark@>
>
> wrote:
>
>>>>The most certain way to make sure that the DDE link works is to
>
> have an
>
>>>>ooPIC S in the loop. Otherwise the high value data and clock
>
> resistors
>
>>>>need to be used. No one can explain this oddity, but it has
>
> something
>
>>>>to do with the PIC 16F877a part.
>>>>
>>>>DLC
>>>
>>>
>>>If you have to use 22k to 33k resistors, the cable length between
>
> the
>
>>>OOPics will have to be measured in small numbers of inches. That
>
> much
>
>>>resistance just won't overcome any kind of capacitance.
>>>
>>>A conventional I2C network would have resistors in the 2.2k range.
>>>
>>>Unfortunately, I only have a couple of S boards so I can't really
>
> test
>
>>>the bug to see what is happening.
>>>
>>>Richard
>>>
>>>
>>>
>>>
>>>
>>>Yahoo! Groups Links
>>>
>>>
>>>
>>
>>--
>>------------------------------------------------------
>>Dennis Clark ooPIC Tech Support
>>www.oopic.com
>>------------------------------------------------------
>>
>
>
>
>
>
>
> Yahoo! Groups Links
>
>
>

--
------------------------------------------------------
Dennis Clark ooPIC Tech Support
www.oopic.com
------------------------------------------------------

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