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TPUG - Toronto PET Users Group
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2008-11-26
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101 lines
├╧═┴╠ ╠┴╬╟╒┴╟┼ ╬╧╘┼╙
┴S WITH ┬ASIC SOME ═┴╔╬
═┼═╧╥┘ LOCATIONS ARE NOT
ESTABLISHED UNTIL THE ACTUAL
RUNNING OF THE PROGRAM. ╘WO
OF THESE, WHICH ARE USED
EFFECTIVELY IN THE ╟╒┼╙╙ ╔╘
PROGRAM ARE LOCATIONS 251 AND
252. ╘HESE CONTAIN THE ╠OW
AND ╚IGH PORTIONS OF THE
ADDRESS OF THE NEXT ─┴╘┴
╙╘┴╘┼═┼╬╘ TO BE READ AFTER
THE EXECUTION OF THE FIRST
╥┼┴─ INSTRUCTION.
╠OC=PEEK(251)+256*PEEK(252)
╘HEREFORE, IF THE VALUES
IN 251 AND 252 ARE SAVED FOR
A PARTICULAR ─┴╘┴ ╙╘┴╘┼═┼╬╘,
BEFORE IT IS READ, YOU CAN
RETURN DIRECTLY TO THAT SAME
DATA STATEMENT READY TO ONCE
AGAIN PERFORM A ╥┼┴─ BY
RESTORING THE SAVED VALUES
INTO 251 AND 252. ╘HIS IS
CALLED A ═┴╥╦ AND ╥┼╙┼╘
OPERATION OR A ├ONTROLLED
╥┼╙╘╧╥┼, WHICHEVER
TERMINOLOGY YOU PREFER.
┴S TO THE INTERNAL
STRUCTURE OF A 'SIMPLE'
(SINGLE ITEM) ─┴╘┴ ╙╘┴╘┼═┼╬╘
IT IS AS FOLOWS:
OFFSET DESC.
-2= ┴DDR ╠OW
-1= ┴DDR ╚IGH
0= ╠INE# ╚IGH
1= ╠INE# ╠OW
2= ╠INE ╠TH
3= ─┴╘┴ ├MD
4= ╙EPERATOR
5= ─ATA ╠TH
6= ─ATA ╔TEM
7= ╘ERMINATOR
8= ╬EXT ├MD
┴DDR ╠OW
9= ╬EXT ├MD
┴DDR ╚IGH
╫HERE 0= THE BYTE
WHICH THE VALUE CONTAINED IN
'╠OC' IS ADDRESSING OR, IF
YOU PREFER, POINTING AT.
╔ HOPE SOME OTHER
COMMAND ENTHUSIASTS WILL FIND
THIS INFORMATIVE.
╔ ALSO HOPE THAT PEOPLE
WHO READ THE ├╧═┴╠ ═┼═╧╥┘ ═┴╨
AND SEE BYTES LISTED AS
'╒NUSED OR ╞REE ═EMORY' WILL
NOT RUSH OUT AND START
STORING LITTLE BITS OF
INFORMATION HERE AND THERE!
╘HEY MAY BE SUPRISED AT HOW
THEIR PROGRAM RUNS, IF AT
ALL!! ╔ WOULD RECOMEND THE
PHRASE '╒╦╬╧╫╬ ╒╙┼' FOR
UNDOCUMENTED BYTES OF MEMORY,
ESPECIALLY IN THE ╨AGE ┌ERO
┴REA.
╞OR AN EXAMPLE OF THE
VALUES IN 251 AND 252 BEING
PUT TO USE PLAY THE GAME
'╟╒┼╙╙ ╔╘' AND WATCH ─┴╘┴
╙╘┴╘┼═┼╬╘╙ BEING DYNAMICALLY
CHANGED BY A RUNNING PROGRAM.