Microchip PIC Forum: [piclist] Re: 12F675 Startup Problems

Hello-

I've had some similar problems with hyperterminal in regards to
startup problems myself. Watch what your initial "power up"
conditions will look like to hyperterminal. If it sees a high
(voltage level) to it's interface, it will assume that there is a
break condition. I have found with bit banging interfaces with the
675, I have had times where the change from the high impedance state
from the driver to actually making the pin an output affects the
other side's operation. After the receiving side sees the start
condition, and failing to find a proper stop condition, a "framing
error" is seen by the receiving side. This can continue for quite a
while. This, of course, has been after determining that the baud
rate of the transmitter is correct......

Depending upon your configuration, you can modify the circuit with
a simple pull up resistor to source power to the interface driver
to present a high voltage state.

Alternatively, you might have some luck with presenting a mark
condition to the interface (a very long stop condition) before sending
the ascii characters.

For testing, you might find some useful information by inserting a
long delay between strings in your test firmware.

Although timing is critical in asynchronous communications, I have
reliably established 9600 baud transmitters in a bit banging
configuration at room temperatures without resorting to a crystal for
timing.

I hope this helps.

Cheers,

Rich S.

--- 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
>