Microchip PIC Forum

Friday, December 7, 2007

[piclist] Re: 12F675 Startup Problems

To make it work I had to change the the value that gets moved into
OSCCAL. Since the serial routine that I used had been around awhile
I can only assume that the problem is in the Pic oscilator. Don't
know what to do to fix it though as I don't want to have to
calibrate each pic chip.

Max

--- In piclist@yahoogroups.com, "kg4pid" <kg4pid@...> wrote:
>
> I'm using a serial routine on a 12F675 and started by sending out
the
> word "HELLO" over and over. Funny thing is while it's powered on I
get
> nothing out, but the instant I remove power it sends out 10 or 11
> characters. The filter cap is powering it for that fraction of a
> second. The circuit is being powered by a 9V battery with a 78L05
to
> regulate it at 5V. My meter reads 4.99v at the pic chip. A logic
probe
> connected to the output blinks the whole time it is powered up
which
> should mean that its sending something. I had to include this bit
of
> code at the very beginning before I got anything at all.
> call 0x3FF ; Retrieve Factory Calibration
> BANKSEL OSCCAL ; BANK1
> movwf OSCCAL
>
> Anyone have any ideas as to what might cause a problem like this?
>
> Thanks, Max
>

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Re: [piclist] Re: 12F675 Startup Problems

Each PIC comes with a different osccal value so you shouldn't have to put a value of your own in there.

Otherwise use an external resonator.

-------Original Message-------

From: kg4pid

Date: 12/07/07 23:33:55

To: piclist@yahoogroups.com

Subject: [piclist] Re: 12F675 Startup Problems

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Thursday, December 6, 2007

Re: [piclist] 12F675 Startup Problems

This may be a baudrate problem, baudrate accidentally coming within spec while the power is on the downslope.
Hyperterminal will usually filter out anything that isn't readable.
Try RS232 Hex Com Tool instead its much better, it'll show you ASCII or HEX, and if you're getting
garbage it'll show you that too.
< http://www.rs232pro.com/ >

kg4pid wrote:

I'm using a serial routine on a 12F675 and started by sending out the
word "HELLO" over and over. Funny thing is while it's powered on I get
nothing out, but the instant I remove power it sends out 10 or 11
characters. The filter cap is powering it for that fraction of a
second. The circuit is being powered by a 9V battery with a 78L05 to
regulate it at 5V. My meter reads 4.99v at the pic chip. A logic probe
connected to the output blinks the whole time it is powered up which
should mean that its sending something. I had to include this bit of
code at the very beginning before I got anything at all.
call 0x3FF ; Retrieve Factory Calibration
BANKSEL OSCCAL ; BANK1
movwf OSCCAL
Anyone have any ideas as to what might cause a problem like this?
Thanks, Max

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Eirik Karlsen

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[piclist] Re: 12F675 Startup Problems

Hi,
you may try to bypass VDD & VSS by an 100nF capacitor as close as
possible to pin 1 & 8. Then don't connect directly pin 1 to 4, but put
a resistor 100K from pin 1(VDD) to pin 4 (MCLR) and a capacitor 100nF
from pin 4 to pin 8 (VSS).
Best regards

--- In piclist@yahoogroups.com, "kg4pid" <kg4pid@...> wrote:
>
> I'm using a serial routine on a 12F675 and started by sending out the
> word "HELLO" over and over. Funny thing is while it's powered on I get
> nothing out, but the instant I remove power it sends out 10 or 11
> characters. The filter cap is powering it for that fraction of a
> second. The circuit is being powered by a 9V battery with a 78L05 to
> regulate it at 5V. My meter reads 4.99v at the pic chip. A logic probe
> connected to the output blinks the whole time it is powered up which
> should mean that its sending something. I had to include this bit of
> code at the very beginning before I got anything at all.
> call 0x3FF ; Retrieve Factory Calibration
> BANKSEL OSCCAL ; BANK1
> movwf OSCCAL
>
> Anyone have any ideas as to what might cause a problem like this?
>
> Thanks, Max
>

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[piclist] Re: USART Transmit Issue

It sounds like a power up problem.

It could be the transmit pin is at a zero before the first byte is sent
causing a recieve error at the PC.

Might be worth putting a pullup on the TX pin.

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[piclist] Re: Re: PROTEL or EAGLE PCB-CAD - comparisons ???

It should be on the PIC datasheet !

Do a search at www.microchip.com

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[piclist] Re: RS232 serial communication problems with 18F458

I usually start by sending out 55H on the transmit pin and scope it to see what the actual bit timing is.
Once the transmit is correct the receive just follows on.

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