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Running a 16F876 @ 20mhz

 
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Running a 16F876 @ 20mhz
PostPosted: Mon Jan 06, 2003 4:53 pm     Reply with quote

Can I run a PIC16F876 @ 20mhz with a 3.6v supply?

Thanks

P.S. I have looked at the spec sheet but being a newbie I want to make sure I am right, thanks.
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Original Post ID: 10480
Newbie
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More questions?
PostPosted: Mon Jan 06, 2003 5:03 pm     Reply with quote

Another question, Most of my other components on my project run at 5v, the reason I want to run the PIC at 3.6v is so I can interface with a GSM that runs at 3.6v and can directly connect to the PIC if the rs232 voltages are = 3.3v.

What is the easiest way to run the PIC at 3.6v whilst running all other components at 5v (appart from the GSM) can I just put some resistors in there?

P.S. I don't want to use another regulator, space & cost. and please be very descriptive as I'm new to electroincs also :O)

E.g. Connect a xxohm resistor to supply pin of pic and another to bla bla bla.

Thanks again.


:=Can I run a PIC16F876 @ 20mhz with a 3.6v supply?
:=
:=Thanks
:=
:=P.S. I have looked at the spec sheet but being a newbie I want to make sure I am right, thanks.
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Original Post ID: 10481
thomas
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Re: More questions?
PostPosted: Mon Jan 06, 2003 5:47 pm     Reply with quote

Don't follow my footstep! I ran the Micro on 4V before and I found that some Micro runs and some doesn't. The sure way is to run the Micro according to the spec.

Buy a level converter IC for level translation. I used transistors and resistors to do this before, but there is always a "gotcha" somewhere...

regards,
Thomas
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Original Post ID: 10484
PCM programmer



Joined: 06 Sep 2003
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Re: More questions?
PostPosted: Mon Jan 06, 2003 7:11 pm     Reply with quote

:=Another question, Most of my other components on my project run at 5v, the reason I want to run the PIC at 3.6v is so I can interface with a GSM that runs at 3.6v and can directly connect to the PIC if the rs232 voltages are = 3.3v.
:=
:=What is the easiest way to run the PIC at 3.6v whilst running all other components at 5v (appart from the GSM) can I just put some resistors in there?
:=
:=P.S. I don't want to use another regulator, space & cost. and please be very descriptive as I'm new to electroincs also :O)
:=
------------------------------------------------------------

T.I. has an appnote on voltage translation.
<a href="http://www-s.ti.com/sc/psheets/scya006/scya006.pdf" TARGET="_blank">http://www-s.ti.com/sc/psheets/scya006/scya006.pdf</a>

For example, the AHCT series will convert from TTL levels
to CMOS levels (when running the AHCT gate at 5v).
You can then choose a single gate package (SOT23-5 package)
from this chart:
<a href="http://www-s.ti.com/cgi-bin/sc/family3.cgi?family=SINGLE-GATES" TARGET="_blank">http://www-s.ti.com/cgi-bin/sc/family3.cgi?family=SINGLE-GATES</a>

Then you can go to Digikey and see if they have it in stock.
For example, search for 74ahct1g04, here:
<a href="http://www.digikey.com/" TARGET="_blank">http://www.digikey.com/</a>

That takes care of the TTL -> CMOS translation. (ie., from GSM
to PIC). Now you have to work on the CMOS to TTL translation.
Perhaps the LVC family will work. Read the appnote above
and follow the same process. (Have to check everything, of
course.)
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Original Post ID: 10486
Pete Smith
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Re: More questions?
PostPosted: Tue Jan 07, 2003 4:04 am     Reply with quote

:=Another question, Most of my other components on my project run at 5v, the reason I want to run the PIC at 3.6v is so I can interface with a GSM that runs at 3.6v and can directly connect to the PIC if the rs232 voltages are = 3.3v.
:=
:=What is the easiest way to run the PIC at 3.6v whilst running all other components at 5v (appart from the GSM) can I just put some resistors in there?
:=
:=P.S. I don't want to use another regulator, space & cost. and please be very descriptive as I'm new to electroincs also :O)
:=
:=E.g. Connect a xxohm resistor to supply pin of pic and another to bla bla bla.

Regards to your 20MHz question - so long as you get a part that's rated at 20MHz (not 4MHz), it'll work.

Regards your other questions - can't you get low voltage versions of the rest of your devices? It'll make your life easier if you can run everything at 3.6v.

One thing that you <u>will</u> have to realise is that if you run the PIC at less than 4.2v (ISTR), you'll have to turn off Brown Out Detect flag, otherwise the PIC may not start, because it thinks the power supply has dropped out (below 4.2v) and will reset the PIC.

The other alternative is to run everything at 5v, except the GSM module, and then make a couple of non-inverting level switchers from a few transistors and resistors.

HTH

Pete.
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Original Post ID: 10497
Sherpa Doug
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Re: More questions?
PostPosted: Tue Jan 07, 2003 9:25 am     Reply with quote

If this GSM uses real RS232 signals and you want to use a hardware UART on the PIC I expect that you will need at least an inverter in the RS232 lines. If you need an inverter, just make it a level shifting inverter (74AC240 maybe?) and run the PIC from 5V along with your other circuitry.

:=Another question, Most of my other components on my project run at 5v, the reason I want to run the PIC at 3.6v is so I can interface with a GSM that runs at 3.6v and can directly connect to the PIC if the rs232 voltages are = 3.3v.
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This message was ported from CCS's old forum
Original Post ID: 10500
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