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'[PIC] Newbie questions: TTL or CMOS?'
2000\06\08@130055 by Nathan Burnside

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<x-flowed>Are the PIC I/O pins TTL or CMOS? The data sheets say that the PICs are
CMOS, but it also says the I/O pins have a TTL buffer. Does this mean that
I need to treat them strictly as TTL? What kind of situations can damage
the I/O pins on a PIC? (aside from the case of voltages over Vdd and under
Vss) If I set an output pin high when it is tied to ground, will it simply
source 20mA without damaging the chip, or will it cause a short to Vdd and
fry the chip? Thanks for your help.

Nathan

</x-flowed>

2000\06\08@192126 by Tony Nixon

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Nathan Burnside wrote:
>
> Are the PIC I/O pins TTL or CMOS? The data sheets say that the PICs are
> CMOS, but it also says the I/O pins have a TTL buffer. Does this mean that
> I need to treat them strictly as TTL? What kind of situations can damage
> the I/O pins on a PIC? (aside from the case of voltages over Vdd and under
> Vss) If I set an output pin high when it is tied to ground, will it simply
> source 20mA without damaging the chip, or will it cause a short to Vdd and
> fry the chip? Thanks for your help.
>
> Nathan

Depends which pin.

Most appear to be TTL in and CMOS out. Some have Schmitt Trigger input,
and there is an Open Collector output usually on RA4.

Because they (not all) are TTL in and CMOS out, I would assume that they
interface directly to TTL and CMOS.

Check out the back of the data sheets for specific IO pin information.

I've had shorts on pins and the chip seems to survive, but this may not
always be the case. Just avoid overloading or overdriving the pins, and
don't rely on them delivering a finite current source. Some appear to
survive reversed supply voltage as well.

The chip is more likely to get damaged by static discharge from you, or
by inductive spikes caused by insufficient protection.

--
Best regards

Tony

http://www.picnpoke.com
spam_OUTsalesTakeThisOuTspampicnpoke.com

2000\06\13@100001 by Don B. Roadman

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On 8 Jun 2000, at 11:59, Nathan Burnside wrote:

> Are the PIC I/O pins TTL or CMOS?

CMOS

>The data sheets say that the PICs
> are CMOS, but it also says the I/O pins have a TTL buffer. Does this
> mean that I need to treat them strictly as TTL?

You can use them as ttl. In that case, use 5V supply.

You can use them with cmos also.

Please read Pic data sheet for electrical specifications, TTL data
sheets for electrical specifications, and cmos data sheets for
electrical specifications. These will illuminate you.

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