Searching \ for '16C74A problem (dual Vdd,Vss??)' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: techref.massmind.org/techref/power/decouple.htm?key=vdd
Search entire site for: '16C74A problem (dual Vdd,Vss??)'.

Truncated match.
PICList Thread
'16C74A problem (dual Vdd,Vss??)'
1999\06\08@230724 by Stewart Pye

flavicon
face
Hi...

I'm testing a project that uses a 16C74A. I've used the 16F84 quite a bit
but this is my first try using the 16C74 with a HS osc at 16Mhz.

Problem:
I cant even get an led to flash. I know the code is correct. I set the osc
to HS.

Question:
Are the two VDD and VSS pins connected internally???
I got 12ohms between the 2 Vss pins but several Mohms between the Vdd pins.
Is this correct??
Should I connect these pins externally???
Is there something else that could be causing the problem?

Any help would be much appreciated. (the frustration's building)

Thanks,
Stewart Pye

1999\06\08@231814 by Chris Eddy

flavicon
face
Stewart:

You realy must connect those pins together and to supply.  I accidentally left
one of the VS's off on a '73 once, and the A/D didn't work right at all.  A
cursory check with a meter saw that pin at ground, or so one would think on a
quick glance.  Turns out that a few tens of mV will whack the A/D.  Connect
them through and to supply, with bypass.

Try a small hello world by killing the watchdog, interrupts, and all
unnecessary calls.  Start small and work up!  You might just read TMR0 and
stuff it onto port C for the fun of it.. Scope should go nuts.  Don't forget
that the portA is set for analog function by default.  Ref ADCON0/1.  And that
RA4 is an open collector all the time.  If you were looking for excitement on
one of these RA pins, you could have the wool over your eyes.

Stewart Pye wrote:

{Quote hidden}

1999\06\08@232703 by Nick Taylor

picon face
Stewart Pye wrote:
<snip>
> I'm testing a project that uses a 16C74A. I've used the 16F84 quite a bit
> but this is my first try using the 16C74 with a HS osc at 16Mhz.

Stewart - -

Download DS30390E from Microchip's site:
  www.microchip.com/10/Lit/PICmicro/16C7X/index.htm
It's got ALL the answers.

Have fun,
- - - Nick - - -

1999\06\08@234349 by g.daniel.invent.design

flavicon
face
check ram base address is corect.

check output pin is not designated as a special function pin from reset.

connect ALL power supply pinz.

DON'T activate security bitz, they won't U.V. erase !

regards,
Graham.


Stewart Pye wrote:
{Quote hidden}

--
Steam engines may be out of fashion, but when you consider that an
internal combustion engine would require recovery of waste heat by
transfer just before top dead centre then fashion becomes rather
redundant, USE STRATIFIED HEAT EXCHANGERS ! and external combustion.

You heard it first from: Graham Daniel, managing director of Electronic
Product Enhancements.
Phone NZ 04 387 4347, Fax NZ 04 3874348, Cellular NZ 021 954 196.

1999\06\09@003621 by Stewart Pye

flavicon
face
I've connected the two Vss pins together and the two Vdd pins. Still got
the same problem. Something weird though....

When I touch the top of the 16C74JW the LED lights up. The LED is active
low. ie: connected between RB0 and +5V with 220ohm R. Should this happen??
It seems strange to me.

Thanks

Stewart Pye

At 11:17 PM 8/06/99 -0400, you wrote:
>Stewart:
>
>You realy must connect those pins together and to supply.  I accidentally
left
>one of the VS's off on a '73 once, and the A/D didn't work right at all.  A
>cursory check with a meter saw that pin at ground, or so one would think on a
>quick glance.  Turns out that a few tens of mV will whack the A/D.  Connect
>them through and to supply, with bypass.
>
>Try a small hello world by killing the watchdog, interrupts, and all
>unnecessary calls.  Start small and work up!  You might just read TMR0 and
>stuff it onto port C for the fun of it.. Scope should go nuts.  Don't forget
>that the portA is set for analog function by default.  Ref ADCON0/1.  And
that
{Quote hidden}

1999\06\09@013126 by Chris Eddy

flavicon
face
Guess number one is some kind of intermittent.

Hunch number two.. Are you using two small capacitors from each leg of your
crystal to ground??  If not, see manufacturers data.  Typical values are 18-22pF
.

Stewart Pye wrote:

{Quote hidden}

1999\06\09@014248 by Tony Nixon

flavicon
picon face
Stewart Pye wrote:

> When I touch the top of the 16C74JW the LED lights up. The LED is active
> low. ie: connected between RB0 and +5V with 220ohm R. Should this happen??
> It seems strange to me.

That's probably a good clue. It sounds like you have floating inputs
that may be causing your problems. Try making any unused port pins
Outputs, and make sure that pins connected as inputs are not tied to
open circuit switches etc without a pullup(down) of some kind.

It happens on my 16C74's. If you touch a spare pin (which is just a
floating input) with a finger, the PIC crashes straight away.

--
Best regards

Tony

'The Engine' - Design your own programmer.

http://www.picnpoke.com
Email spam_OUTpicnpokeTakeThisOuTspamcdi.com.au

1999\06\09@040749 by Joe McCauley

picon face
Try clearing all memory locations at startup.

Joe

At 14:05 09/06/99 +1000, you wrote:
{Quote hidden}

on a
>>quick glance.  Turns out that a few tens of mV will whack the A/D.  Connect
>>them through and to supply, with bypass.
>>
>>Try a small hello world by killing the watchdog, interrupts, and all
>>unnecessary calls.  Start small and work up!  You might just read TMR0 and
>>stuff it onto port C for the fun of it.. Scope should go nuts.  Don't forget
>>that the portA is set for analog function by default.  Ref ADCON0/1.  And
>that
>>RA4 is an open collector all the time.  If you were looking for
excitement on
{Quote hidden}

pins.
{Quote hidden}

1999\06\09@193135 by Brian Kraut

picon face
Sounds like you are having problems with light getting in the window and messing
with your ram locations.  I bet your problem will go away if you put a sticker o
n
the window.  I have had this problem a few times although I normally leave the
window uncovered and it is O.K. almost all te time.

Stewart Pye wrote:

{Quote hidden}

1999\06\09@214216 by Lau Chi Cheung, Samuel

flavicon
face
Dear Stewart,

I think you can find the answer from the book
"Design with PIC Microcontrollers" by John B. Peatman
or try to email to
.....john.peatmanKILLspamspam@spam@ece.gatech.edu

Regards,
Samuel Lau

Stewart Pye wrote:

{Quote hidden}


'16C74A problem (dual Vdd,Vss??)'
1999\09\07@163908 by Larry G. Nelson Sr.
flavicon
face
Connect all the power and ground pins to insure proper operation. Sometimes
the oscillator will not start and run reliably and you need to adjust the
caps slightly for reliable startup and oscillation. Also check the type of
crystal you are using. You may be overdriving it and need a resistor to the
crystal.


At 01:10 PM 6/9/99 +1000, you wrote:
{Quote hidden}

Larry G. Nelson Sr.
L.NelsonspamKILLspamieee.org
http://www.ultranet.com/~nr

1999\09\07@224545 by Jim Robertson

flavicon
face
Are you using any of the Analog pins? You must convert them to digital I/O
first with this code.

       BSF STATUS,RP0
       MOVLW 07H
       MOVWF 01FH
       BCF STATUS,RP0

Maybe this might help.

-Jim



{Quote hidden}

Regards,

Jim Robertson
NEWFOUND ELECTRONICS
________________________________________
Email: EraseMEnewfoundspam_OUTspamTakeThisOuTpipeline.com.au
http://www.new-elect.com
MPLAB compatible PIC programmers.
________________________________________

More... (looser matching)
- Last day of these posts
- In 1999 , 2000 only
- Today
- New search...