A86: Re: Re: More ASM Questions
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A86: Re: Re: More ASM Questions
OK its clearer now. I was thinking of using a getky routine and
reading a certain number of keypresses. Here's my idea. Could you tell
me if my logic's right?
Start:
call _clrLCD
call _runindicoff
ld b,$04
KeyLoop:
push bc
call GET_KEY
pop bc
cp K_NOKEY
jr z, KeyLoop
push af
djnz KeyLoop
I first initialize B to 4 or $04. I push B to the stack, call the
GET_KEY ROM Routine, pop BC from the stack, see if any keys were
pressed, if not then loop again but save the key that was pressed from
the port by pushing it on the stack then loop over until B=0. I know
that I should check for other keys and that there should be other code
around it.
Really after that I could pop af every time to compare its value to a
key like so
pop af
cp K_3
jr nz, Start
Am I doing this right. I'm trusting that such operatives as jr nz and
djnz are correct. I haven't tried this or compiled it yet. I just
wrote it. What exactly does djnz do? I'm pretty sure this will work
from looking at others source code.
I'm just curious and anxious to learn. (Did you notice no HTML?) I'd
like to apologize again.
-----Original Message-----
From: David Phillips <david@acz.org>
To: assembly-86@lists.ticalc.org <assembly-86@lists.ticalc.org>
Date: Saturday, January 23, 1999 9:12 PM
Subject: A86: Re: More ASM Questions
>
>The "stack" that computers use is a LIFO queue--last in, first out.
This
>means that the last value "pushed" will be the value "popped". You
can
>think of it like a stack of plates in a cafeteria. If you put a red
plate
>on the stack, the put blue plate on, then take off a plate, you will
get the
>blue plate back. If you take off another plate, you will get the red
plate
>back. When ever you "pop" something, it is removed from the stack.
>
>The calc's stack only works with values, not registers. However, you
can
>only push registers, not values. When you push a register, the value
of the
>register is placed on the stack. When you pop a value off the stack
into a
>register, the value is moved from the top of the stack into the
register.
>The register it was pushed from doesn't matter in the slightest,
because
>only the value is stored on the stack. For example, to move the
value in HL
>into IX:
>
>push hl ; the value in HL is "pushed" onto the stack
>pop ix ; the value on the stack is "popped" off into IX
>
>Note that HL still contains the original variable, but IX has the
same thing
>HL has. When pushing, the value is only copied, it is not changed.
Now,
>the order of pushing and popping can be important if you are using
the stack
>to save your registers (a common use of the stack). Since it is
LIFO, you
>must pop in the reverse order that you pushed, or else the values
will be
>all messed up:
>
>push af ; AF is now on the top of the stack (...AF)
>push bc ; BC is now on the top, AF is below it (...AF, BC)
>push de ; DE is on top of BC, which is on AF (...AF, BC, DE)
>
>...code here...
>
>pop de ; since DE is on top of the stack, it is popped first
(...AF, BC)
>pop bc ; BC is now on top, so it is popped next
(...AF)
>pop af ; the top is now AF, so pop it last
(...)
>
>The dots represent the other data on the stack. The stack area
"below" what
>you push will contain other data, such as where your program will
RETurn
>when it is done.
>
>A quick warning about the stack is that you must ALWAYS pop for every
time
>that you push. CALL/RET use the stack. Think of CALL as a push and
RET as
>a pop, so you can't push stuff, call a routine, then pop stuff in
that
>routine, or it will mess up. If you push stuff and don't pop it,
then try
>to RETurn from the program, RET will pop the wrong data from the
stack (your
>data, not the return address) and will jump to an invalid locatin,
thus
>crashing the calc!
>
>So, if your program crashes for no reason, count your pushes and
pops!
>
>--
>David Phillips <david@acz.org>
>http://www.acz.org/
>
>----- Original Message -----
>From: Chris Flanigan <cflan@granitecity.com>
>To: 86 Assembly <assembly-86@lists.ticalc.org>
>Sent: Saturday, January 23, 1999 4:07 PM
>Subject: A86: More ASM Questions
>
>
>>
>>Sorry for all of the questions. I just want to learn this langauge.
>>
>>I have a question about the logic of using the stack.
>>
>>If I push AF on the stack my stack would "look" like this
>>
>>AF
>>
>>If I push BC on the stack, my stack would now "look" like this
>>
>>BC
>>AF
>>
>>Is this correct?
>>
>>If I popped BC would the stack look like this
>>
>>AF
>>BC
>>
>>I don't really understand this. Again, I know its simple but...
>>
>>I will learn this language, oh yes. It may take me time but I'll one
day
>>get it.
>>
>>Thanks for everyones help and cooperation.
>>
>>This message was written by Chris Flanigan.
>>
>>If this is in reply to an inquiry about the TI Archive, direct
>>all e-mail to ti_archive@hotmail.com.
>>
>>If this is a personal message, direct all e-mail to
cflan@granitecity.com
>>
>>
>>
>
>