PIC Assembler 16F872 LCD 2x16 Hitachi Clocking

[Regular Guy]

Why do we have to 'Clock' it?

Here is Clock subroutine.

Thanks!

[Regular Guy]

Here is Clock used in 'Display Configuration'.

[Regular Guy]

Here is explanation for it from book.

[Jerson]

Simple explanation I can suggest

Since the data bus on which your commands are being sent out could also be used for other devices, the data that needs to go to the LCD needs to pass through a gate. This gate is opened and closed by the clock pulse. This keeps the LCD sane.

[Ttelmah]

However the point is that this could be done just as well in C as assembler.
CLOCK here is a label, so the 'name' that the function is given.

In MPASM, a 'Label', _must_ start in column 1, and _may_ be followed by a
colon.
So 'CLOCK' is the name of this function.

So the function can be called with:

CALL CLOCK

If you have PORTB as a #byte, then the C:

[Regular Guy]

Thank you Jerson

Simple works for us.

Thank you Ttelmah

Right now we must stay with assembler.
_________________
PIC Hobbyist

[temtronic]

curious am I ...

this...

[Regular Guy]

Thank you temtronic

Here is 'definition' for RETLW in back of book.

Section in back of book is author's 'definition's' for instructions.

PIC In Practice David W Smith

[temtronic]

I do know what the instruction does, been 'playing with PICs' long before CCS C came out.., but don't know why it's there.

portion of code...

[Ttelmah]

You would have to look at what DELAYP1 does. This might be using W.
However RETLW takes no more time than a RETURN, and does therefore
provide a 'zero cost' way of clearing W, so the programmer may have
just got into the habit of using this.

[Regular Guy]

Thank you Ttelmah

Ah hah!

It is a COMBINATION instruction.

A RETURN and a MOVLW

Literal being loaded to or into W is 0

Very sharp catching that and pointing it out.

We had just laid it off to it was a 'Good Practices' thing.

Never really thought about it much though.

Thanks!

EDIT:

We caught two things you said

1 'No Cost' thing to do

2 Clears W register

Yes. low cost is good and clearing registers does play into things.

Cleared registers can reduce 'Erratic behavior' and 'Unexpected Results'

and straight out bugs.
_________________
PIC Hobbyist

[Ttelmah]

Though (of course), you have to be aware that the effect can be
adverse.
Assume you have a code sequence that sets W up with something before
the routine, then the programmer looks at the functions 'inside' the
subroutine, and thinks "bit sets, nops, so no change to W", but misses
the RETLW. Result W is not what is expected....
The RETLW is very commonly used in CCS for the more basic PIC's
as a way of storing const values. You just have a sequence of these
for all the values, and in front of this, have code that just adds the
entry number required to the PC. Call this, and it returns with the required
value. On PIC's that don't have any way to directly read their ROM,
this is the only way to do this...

[Regular Guy]

Thank you Ttelmah

Most of what you say is ahead of what we are doing.

BUT

There is a 7 Segment LED lesson in the book

It has a 'Lookup Table' . For each number.As you would think.

That may be a little of what you are talking about.

Let me post the RETLW part of 7 segment program.

[Ttelmah]

Yes, that is doing exactly this. Using the RETLW instructions as a way
to give a lookup from ROM.