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'Serial programmer question'
1995\12\15@182859 by Patrick C Leger

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Hi,

I just built an RS-232 powered 16C84 programmer (the one with 1
diode, 1 cap, 1 78L05, and 3 resistors), but I'm having some problems
with it.  The 78L05 sucks the tx line (and thus MCLR) down to about 7
volts, which is apparently not enough to kick it into programming
mode.  I verified this behavior with another 78L05 running on the
serial line, driving only a 4.7K resistor + smoothing cap; when
nothing is connected to the serial line, I get about 12V on it; when
the 78L05 is connected, I get from 5 to 7V depending on the 78L05's
load.

Am I incorrect in thinking that the '84 needs 12V on MCLR to put it
into programming mode?  All the other signals to the chip looked fine.
Or do I just have a cheesy 78L05?  It's made by JRC/NJR.

--
Chris Leger (spam_OUTblahTakeThisOuTspamcmu.edu)
Carnegie Mellon University
Field Robotics Center

1995\12\15@191541 by Rolan

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On Fri, 15 Dec 1995, Patrick C Leger wrote:

> Hi,
>
> I just built an RS-232 powered 16C84 programmer (the one with 1
> diode, 1 cap, 1 78L05, and 3 resistors), but I'm having some problems
> with it.  The 78L05 sucks the tx line (and thus MCLR) down to about 7
> volts, which is apparently not enough to kick it into programming
> mode.  I verified this behavior with another 78L05 running on the
> serial line, driving only a 4.7K resistor + smoothing cap; when
> nothing is connected to the serial line, I get about 12V on it; when
> the 78L05 is connected, I get from 5 to 7V depending on the 78L05's
> load.
>
> Am I incorrect in thinking that the '84 needs 12V on MCLR to put it
> into programming mode?  All the other signals to the chip looked fine.
> Or do I just have a cheesy 78L05?  It's made by JRC/NJR.
>

It is true the specs call for 12 or 13 Volts on the MCLR pin, but those
are the just the specs ;)

In reality, the PIC can go into the program mode with much less. I think
my serial port surfs on the edge of 7-9 volts during programming. Rather
than pulling apart your circuit, you might want to try a serial port
on a different computer.

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Rolan Yang            http://hertz.njit.edu/~rxy5310   Electrical Engineer
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4 out of 10 people are annoyed by ^ this.

1995\12\15@193649 by Arne Alsvik

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At 18:25 15.12.95 -0500, you wrote:
>Hi,
>
>I just built an RS-232 powered 16C84 programmer (the one with 1
>diode, 1 cap, 1 78L05, and 3 resistors), but I'm having some problems
>with it.  The 78L05 sucks the tx line (and thus MCLR) down to about 7
>volts, which is apparently not enough to kick it into programming
>mode.  I verified this behavior with another 78L05 running on the
>serial line, driving only a 4.7K resistor + smoothing cap; when
>nothing is connected to the serial line, I get about 12V on it; when
>the 78L05 is connected, I get from 5 to 7V depending on the 78L05's
>load.
>
>Am I incorrect in thinking that the '84 needs 12V on MCLR to put it
>into programming mode?  All the other signals to the chip looked fine.
>Or do I just have a cheesy 78L05?  It's made by JRC/NJR.
>


I do connect a power supply between 7805 and the diode (I use not a 78l05).

Arne -Norway

1995\12\15@193856 by Arne Alsvik

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At 18:25 15.12.95 -0500, you wrote:
{Quote hidden}

I do connect a power supply between 7805 and the diode (I use not a 78l05).

Arne -Norway

1995\12\18@094219 by Rick Miller

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Patrick C Leger wrote:
>
> Hi,
>
> I just built an RS-232 powered 16C84 programmer (the one with 1
> diode, 1 cap, 1 78L05, and 3 resistors), but I'm having some problems
> with it.  The 78L05 sucks the tx line (and thus MCLR) down to about 7
> volts, which is apparently not enough to kick it into programming
> mode.

Chris,

Check your regulator ...is it really a 78*L*05?
It should be just the same size as an ordinary transistor.

I built my first PicBlaster with a 7805 (no "L") and had identical
results.  Make sure you're using the "L"ow-power regulator.
--
Rick Miller    <http://www.execpc.com/~rdmiller>

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