"What''s a Microcontroller" Chapter 4 project 1

Archiver

Lu Kwan:

I haven't time just now to read your code in detail, but let me give you a
quick suggestion. Tomorrow I'll look it over more carefully to see if I can
add anything. For now:

The requirement that the Stamp wake up refusing commands defines an initial
state, but this condition also arises during execution. You have one mode of
operation (refusing commands), but more than one way to reach that mode.
That's a sign you should use a subroutine. That way, if you change the
behavior you only need to change the code in one place to affect all the
ways you can initiate that behavior. (Sorry if that's not clear. It's late
and I have to hurry.)

So open your program with a statement that calls the subroutine:

GOSUB WaitForStartButton

Then write a subroutine:

WaitForStartButton:
[noparse][[/noparse]...]
RETURN

Now the subroutine must satisfy the requirements of the mode it services. If
I remember what you said in my quick reading, you must display a message on
the debug terminal screen and then wait for the start key. Something like
what you wrote:

> DO WHILE IN0 = 0
> DEBUG "Press Start switch to start the machinery",CR, CRSRUP
> LOOP

will probably work. (I'd have to check what you said about how the switch is
connected to see if de-bouncing is necessary. I doubt it, so this is
probably fine to detect the switch.) However, the technique is what we might
call "inelegant" -- not to be prissy, but because it does unnecessary work
by sending those characters to the debug screen over and over. Even worse, I
suspect it will annoy the user by making the display flicker as you write
that message repeatedly.

Try this order of commands instead:

> DEBUG "Press Start switch to start the machinery",CR, CRSRUP
> DO WHILE IN0 = 0
> LOOP

Now we have:

WaitForStartButton:
DEBUG "Press Start switch to start the machinery",CR, CRSRUP
DO WHILE IN0 = 0
LOOP
RETURN

Elsewhere in the code, you detect a "kill" switch. I don't remember how you
said that was detected, so bear with my "meta code" below. That's how we
speak of a step we haven't bothered to code yet, or that may change in
different circumstances. It is "meta code" instead of detailed code.

At that point, you would break off execution of commands like this:

IF <Kill switch pressed> THEN GOTO WaitForStartButton

Good luck for now. As I say, I'll take another look tomorrow if I get any
time at all.

Gary