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PICList Thread
'One pin interface'
1998\01\29@084913 by Morgan Olsson

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Have anyone designed a one pin interface?

It would be nice to have a simple monitor suopport program in every PIC, so
if we want to check inside it when it is working (or working wrong) we can
attach a specialised unit with a display and keyboard to it. We must use
minimum number of pins for it (one), and it should be possible to implement
"everywhere".

The monitor unit I believe can be built using a F84, LCD and a few keys to
select adress and view and change registers, force gotos or calls to
stop,test,run routines etc in the target system.

The target system«s routine shoud of course be as possible as possible, and
perform som kind of erroer check so it don«t treat noise as instructions.

The monitor scans the keys, decode it to simple instructions and send them
to the target. The target sends back register contents binary, which the
monitor decodes and displays.

/Morgan O




Morgan Olsson, MORGANS REGLERTEKNIK, Sweden, ph: +46 (0)414 70741; fax 70331
-

1998\01\29@115416 by SHAWN ELLIS

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{Quote hidden}

Ever heard of an ICE?

1998\01\29@123847 by Tom Mariner

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Hello Morgan,

We generally design in a two pin interface to our Pic projects -- it's
called RS-232 full duplex send / receive. The interface is active in a
real-time mode in the full production versions if possible. I guess if you
wanted just send or just receive it would qualify as one pin. After having
invented lots of standards for wired and wireless serial protocols we have
decided to use standards whenever possible. RS-485 works great too, but is
a little more load on the processor.


Tom

Have anyone designed a one pin interface?

It would be nice to have a simple monitor suopport program in every PIC, so
if we want to check inside it when it is working (or working wrong) we can
attach a specialised unit with a display and keyboard to it. We must use
minimum number of pins for it (one), and it should be possible to implement
"everywhere".

The monitor unit I believe can be built using a F84, LCD and a few keys to
select adress and view and change registers, force gotos or calls to
stop,test,run routines etc in the target system.

The target system?s routine shoud of course be as possible as possible, and
perform som kind of erroer check so it don?t treat noise as instructions.

The monitor scans the keys, decode it to simple instructions and send them
to the target. The target sends back register contents binary, which the
monitor decodes and displays.

1998\01\29@134212 by davewave

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There is lots of code out there for async communications. Implementing a
bi-directional serial interface on one wire is a little tricky, though. Just
define the timing and communication protocol before you start writing PIC code.
Look at some other 1-wire interface schemes for ideas. However, a 2-wire
interface is much, much easier to implement!

Reading and writing the register contents is easy using indirect addressing. I
implemented this in a 16C74 that was used to control battery charging and power
management for a portable PC design. I used the PSP for the interface to the ISA
bus. A low-power PAL decodes the (single) IO address. The BIOS has the ability
to control some aspects of the PIC's functions, it is able to read all registers
in the PIC, and also write to some of the registers (the PIC code was designed
to ignore attempted writes except to a block of about 16 locations).

This made it possible to add APM support to the computers BIOS. Unfortunately, I
cannot provide any code - the client owns it.

I doubt it is possible to implement other ICE functions this way. Other than
brute force (loading the PC with received data) I don't think program flow
control is at all possible.

Good luck with your project.

Dave


Morgan Olsson wrote:

{Quote hidden}

1998\01\29@144457 by Morgan Olsson

picon face
>> Have anyone designed a one pin interface?

>Ever heard of an ICE?

Can«t afford 100 ICE units spread around the customers...
And they don«t fit into the box.
And dont run on that little battery.
And the costomers then would have to learn a lot more to be able to edit
simple parameters.

What I want is more like a attachable keyboard and display, where the most
user interface processing is done in that unit, so the code in target is
small and don«t use much execution time. And driven by as little pinning
and cheap connector and other hardware (any?) as possible, since it would
be nice to leave this option also in production. Nice for in-field testing,
parameter change, loggs read from EPROM, if the target is a C84.

If it works good I plan to use it as normal display for one project too!

Multitasking
It is possible to let it not interfere with the running processes, since it
can be hooked onto a moderately fast timer interrupt.

Protocol
I have some suggestions, (or a lot rather) in a bunch of handwritten pieces
of paper. Roughly, the target is the master, so it decides the speed, and
don«t have to keep listening or synchronizing.
Word sync = long time low out
Start of one bit exchange= rise signal.
One unit later change output to desired output.
The slave samples it two time units after start.
The master change to input three time units after start
The slave outputs it«s bit between four and eight time units after start,
else always tri-state.
The master latches it six time units after start.
Twelve time units after start the master change to output again;
outputtinh high if between bits; low if between words.

The slave selects the speed automatically by measuring synk and selecting
timing multiplier from a table of allowed sets.

How about that?

/Morgan
Morgan Olsson, MORGANS REGLERTEKNIK, Sweden, ph: +46 (0)414 70741; fax 70331
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1998\01\30@021127 by wft

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Morgan

If you can define and create the code that goes in the target PIC to
support the external module that queries it, then I would be willing to
create some external hardware and software to talk to the chip.

I have used PICs with LCDs, serial com and more so it should be
straightforward for me. I have talked to other engineers before about
tethered processing.  This concept assumes you have a very small kernel
of logic in the target that is sufficient to investigate everything in
the target system (maybe not in real time) and most of the computing
burden falls on the device talking to the target [said device could be
another PIC with display/keypad....or a PC or a PDA   or ???]

What do you think?

Gus
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1998\01\30@051810 by wwl

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On Thu, 29 Jan 1998 11:53:20 EST5EDT, you wrote:

{Quote hidden}

Ever heard of poor people?

    ____                                                           ____
  _/ L_/  Mike Harrison / White Wing Logic / EraseMEwwlspam_OUTspamTakeThisOuTnetcomuk.co.uk  _/ L_/
_/ W_/  Hardware & Software design / PCB Design / Consultancy  _/ W_/
/_W_/  Industrial / Computer Peripherals / Hazardous Area      /_W_/

1998\01\30@051813 by wwl

picon face
On Thu, 29 Jan 1998 14:30:52 +0100, you wrote:

>Have anyone designed a one pin interface?
>
>It would be nice to have a simple monitor suopport program in every PIC, so
>if we want to check inside it when it is working (or working wrong) we can
>attach a specialised unit with a display and keyboard to it. We must use
>minimum number of pins for it (one), and it should be possible to implement
>"everywhere".
>
>The monitor unit I believe can be built using a F84, LCD and a few keys to
>select adress and view and change registers, force gotos or calls to
>stop,test,run routines etc in the target system.
>
>The target system«s routine shoud of course be as possible as possible, and
>perform som kind of erroer check so it don«t treat noise as instructions.
>
>The monitor scans the keys, decode it to simple instructions and send them
>to the target. The target sends back register contents binary, which the
>monitor decodes and displays.
I'd use half-duplex async, either using pin tri-stating or pseudo-open
drain. If the data is only sent 'on request' there's no uncertainty of
which direction you need at any given time.
    ____                                                           ____
  _/ L_/  Mike Harrison / White Wing Logic / wwlspamspam_OUTnetcomuk.co.uk  _/ L_/
_/ W_/  Hardware & Software design / PCB Design / Consultancy  _/ W_/
/_W_/  Industrial / Computer Peripherals / Hazardous Area      /_W_/

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