>Hello.
Cut..
>Again, sorry. I wish I could turn back the clock.
>
Yer. I know the feeling.

>Now to the topic...
>
>I want to be able to do some in circuit serial (re)programming of a
>circuit I have. In general, I want to experiment with the fact that a '84 can
>be programmed whilst in the target circuit.
>The circuit consists of a 16c84, vdd is directly connected to vpp.
>
>Now my question is, is this possible? I personally don't think so
>'coz vdd needs to be 5v and vpp needs to be 13.5v.
>I think I will blow it up while trying to program this circuit.
>But maybe not, I don't want to throw away my picstart 16b, nor the '84.


>Is it possible with extra circuitery?

>Should the circuit contain an extra resistor between vdd and vpp and if yes
>what value?

Yes. The value can be 4K7-22K. 10K is good. Some people use a diode but a
resistor is better as it allow ESD to discharge. ESD on the Vpp pin CAN
scramble the memory!

>
>How long can the programmer to '84 cable be in general?
>I want to be able to use quite a long cable (1 meter), are there any things
>I should be aware of?

I meter long cable probably won't cause to many problems but this is a
matter I'm not expert on. There is nothing extra to consider just because
you are actually programming a chip. The usual data comms considerations
apply. I'm to uneducated to say much more.

>I was also wondering, has the picstart16b1 the ability to do in circuit
>serial programming or do I need a special programmer?
>If yes, what kits are out there with this ability? (commercial and diy)

The PICSTART 16B used the serial method of programming (I think!) BUT this
is not necessarily the same as ISP. Maybe you can experiment and get the
PICSTART to program in-system.

It should be possible. Just don't load RB6 and RB7 on the target.

I recommend you start with the 16C84 in a bare socket (and the Vdd-Vpp
resistor) and bring GND (5), Vdd (15), Vpp (4)  RB6 (13) and RB7(14) across
to it. Get it working in the socket first to verify the use of the serial
program method and correct wiring THEN transpose to you target. This way you
can track where problem occur. Pin numbers in () are for the 16C84.

There are many kit programmers that will program the 16C84 in-system but I
feel you should be able get the PICSTART to do what you want.
>
>Many questions, I hope one of you specialists can help me.

Me, a "specialist?" A title at last?!
>
>Thanks in advance.
>

Regards and good luck,

Jim