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═ACHINE ╠ANGUAGE LESSON FOR BEGINNERS #3

─ATE - ═ARCH 17, 1994

╘IME - 10:30 PM ┼╙╘

<[╘ONY] ┴.╘╧╠╠┼> ╧K, THE LAST THING WE WERE COVERING LAST WEEK WAS THE CONCEPT
OF MNEMONIC INSTRUCTIONS LIKE THE "╠─┴" INSTRUCTION IN ═╠.

<[╘ONY] ┴.╘╧╠╠┼> ═NEMONICS ARE THE CONVENTIONAL ABBREVIATIONS FOR TYPING IN ═╠
INSTRUCTIONS WHEN USING AN ASSEMBLER OR AN ═╠ MONITOR.

<[╘ONY] ┴.╘╧╠╠┼> ╘HEY HAVE NO REAL RELATIONSHIP TO THE ACTUAL INSTRUCTION,
WHICH IS JUST A NUMBER, EXCEPT THAT THEY JUST REPRESENT THE INSTRUCTION SO
THAT WE DON'T HAVE TO REMEMBER ALL THE DIFFERENT NUMBERS FOR THE COMMANDS.

<╟┼╧╙-╘╔═> AFK

<[╘ONY] ┴.╘╧╠╠┼> ╘HE "╠─┴" INSTRUCTION HAS SEVERAL DIFFERENT FORMS, ALL OF
WHICH ARE REPRESENTED BY THE "╠─┴" MNEMONIC (╠OA─ ┴CCUMULATOR).

<[╘ONY] ┴.╘╧╠╠┼> ╞OR EXAMPLE, THE TWO INSTRUCTIONS ╠─┴ #$05 AND ╠─┴ $05 ARE
DIFFERENT INSTRUCTIONS BUT BOTH LOAD THE ACCUMULATOR REGISTER WITH SOME SORT
OF DATA.

<[╘ONY] ┴.╘╧╠╠┼> ╞RANK, YOU DOWNLOADED THE "MEGAMON" MONITOR PROGRAM, CORRECT?

<[╞RANK] ┬╒╞╞.╨╚╧╧╬> YES

<[╘ONY] ┴.╘╧╠╠┼> ╧K, WELL TONIGHT ╔ WILL GIVE YOU AN EXAMPLE ═╠ PROGRAM TO TRY
OUT WITH THE MEGAMON MONITOR.

<[╘ONY] ┴.╘╧╠╠┼> ╔T IS PERHAPS THE BEST WAY TO TEACH BOTH THE CONCEPT OF AN ═╠
PROGRAM AND HOW TO USE THE MONITOR.

<[╘ONY] ┴.╘╧╠╠┼> ╘HE MEGAMON PROGRAM IS STORED ON DISK UNDER THE NAME
"MEGAMON.40950".  ╘HE REASON THIS NAME IS USED IS BECAUSE 40950 IS THE MEMORY
ADDRESS THAT MEGAMON LOADS INTO MEMORY AT WHEN YOU ╠╧┴─ THE PROGRAM.

<[╘ONY] ┴.╘╧╠╠┼> ╘O LOAD IT YOU MUST TYPE LOAD"MEGAMON.40950",8,1 AND PRESS
╥┼╘╒╥╬.  ┘OU MUST REMEMBER TO PUT ",8,1" AT THE END OF THE ╠╧┴─ COMMAND TO
LOAD THE PROGRAM IN AT THE CORRECT ADDRESS.

<[╘ONY] ┴.╘╧╠╠┼> ╧NCE THE PROGRAM IS LOADED, YOU SHOULD IMMEDIATELY TYPE THE
COMMAND ╙┘╙40950 AND PRESS ╥┼╘╒╥╬.  ╘HIS TELLS ┬┴╙╔├ TO ACTUALLY START RUNNING
THE ═╠ PROGRAM THAT IS IN MEMORY AT ADDRESS 40950.

<[╘ONY] ┴.╘╧╠╠┼> ╫HEN THE PROGRAM RUNS, YOU WILL SEE THE SCREEN CLEAR AND THE
MONITOR WILL PRINT AN INTRODUCTION AND THEN A PROMPT FOR YOU TO TYPE INPUT.

<[╘ONY] ┴.╘╧╠╠┼> ┘OU WILL SEE A LINE ABOVE THE CURSOR THAT LOOKS SOMETHING
LIKE THIS:

<[╘ONY] ┴.╘╧╠╠┼>    PC  AR XR YR SP SR <[╘ONY] ┴.╘╧╠╠┼> ; 9FFF 05 20 32 F0 30

<[╘ONY] ┴.╘╧╠╠┼> ╘HE NUMBERS LIKE THE "9FFF" PROBABLY WON'T BE THE SAME AS ╔
HAVE RIGHT HERE.

<[╘ONY] ┴.╘╧╠╠┼> ╫HAT THESE TWO LINES TELL YOU IS THE VALUES OF ALL THE
INTERNAL REGISTERS... ╘HE PROGRAM COUNTER (╨├), ACCUMULATOR (┴╥), ╪ REGISTER
(╪╥), ┘ REGISTER (┘╥), ╙TACK POINTER (╙╨), AND STATUS REGISTER (╙╥)

<[╘ONY] ┴.╘╧╠╠┼> ╘HIS IS A DIAGNOSTIC TOOL FOR CHECKING YOUR ═╠ PROGRAM TO SEE
IF IT IS RUNNING CORRECTLY.

<[╘ONY] ┴.╘╧╠╠┼> ┘OU CAN RUN A SHORT SECTION OF THE PROGRAM AND THEN EXAMINE
THE REGISTERS TO SEE IF THEY ARE CURRENTLY HOW THEY ARE SUPPOSED TO BE.

<[╘ONY] ┴.╘╧╠╠┼> ╧K, NOW ╔ WILL SHOW YOU WHAT COULD BE ONE OF THE SHORTEST ═╠
PROGRAMS.  ╘O ACTUALLY "ASSEMBLE" AN ═╠ PROGRAM IN MEMORY, WE USE THE "┴"
COMMAND IN THE MONITOR.

** <[┼DDIE] ┼.┬╧╒╥─╧╬1> IS HERE.

<[╘ONY] ┴.╘╧╠╠┼> ╚IYA ┼DDIE.

<╟┼╧╙-╘╔═> ╚I ┼DDIE

<[┼DDIE] ┼.┬╧╒╥─╧╬1> ╚I ╘ONY,╘IM, ╞RANK

<[╞RANK] ┬╒╞╞.╨╚╧╧╬> 'LO ┼DDIE

<[╘ONY] ┴.╘╧╠╠┼> ╞OR NOW, MOST OF OUR PROGRAMS WILL BEGIN AT ADDRESS $C000,
WHICH IS 49152 IN DECIMAL.  ╘HIS IS A CONVENIENT LOCATION BECAUSE IT DOESN'T
INTEREFERE WITH OTHER PROGRAMS IN MEMORY.

<[╘ONY] ┴.╘╧╠╠┼> ╙O TO TYPE IN THIS PROGRAM YOU WOULD TYPE:

<[╘ONY] ┴.╘╧╠╠┼> ┴ $├000 ╠─┴ #$10

<[╘ONY] ┴.╘╧╠╠┼> AND PRESS ╥┼╘╒╥╬.

<[╘ONY] ┴.╘╧╠╠┼> ╘HIS MEANS TO START ASSEMBLING AN ═╠ PROGRAM AT $C000 AND THE
FIRST INSTRUCTION IS ╠─┴ #$10.

<[╘ONY] ┴.╘╧╠╠┼> ╘HE COMPUTER WILL RESPOND BY PRINTING:

<[╘ONY] ┴.╘╧╠╠┼> ┴ $├002

<[╘ONY] ┴.╘╧╠╠┼> AND THEN DISPLAYING THE CURSOR RIGHT AFTER THE $C002.

<[╘ONY] ┴.╘╧╠╠┼> ╘HIS TELLS YOU TWO THINGS:  ╘HE COMPUTER ACCEPTED YOUR FIRST
INSTRUCTION, AND NOW IT IS READY FOR ANOTHER INSTRUCTION (NOTICE THAT THE
ADDRESS INCREASED BY TWO, BECAUSE THE ╠─┴ #$10 INSTRUCTION TAKES UP TWO
BYTES).

<[╘ONY] ┴.╘╧╠╠┼> ╥EMEMBER THAT THE PROGRAM ISN'T ACTUALLY RUNNING RIGHT NOW,
BUT YOU ARE JUST ENTERING IT INTO MEMORY USING THE MONITOR'S MINI-ASSEMBLER TO
CONVERT THE MNEMONIC INSTRUCTIONS (I.E. THE ╠─┴ INSTRUCTION) INTO THE PURE ═╠
NUMBERS.

<[╘ONY] ┴.╘╧╠╠┼> ╬EXT YOU WOULD TYPE:

<[╘ONY] ┴.╘╧╠╠┼> ┬╥╦

<[╘ONY] ┴.╘╧╠╠┼> AND PRESS ╥┼╘╒╥╬.  ╘HIS ENTERS IN THE ┬╥╦ (┬╥EA╦) INTO
MEMORY.  ═ESSAGE SENT TO ╩OB 4

<[╘ONY] ┴.╘╧╠╠┼> ╘HE ┬╥╦ INSTRUCTION IS SIMPLY AN INSTRUCTION THAT TELLS THE
PROCESSOR TO INTERRUPT THE CURRENT PROGRAM AND START EXECUTING AN ═╠ PROGRAM
AT A DIFFERENT ADDRESS.

<[╘ONY] ┴.╘╧╠╠┼> ╔T IS USED IN ═╠ MONITORS TO END THE PROGRAM AND RETURN
CONTROL TO THE MONITOR, WHERE IT WILL DISPLAY THE VALUES OF THE REGISTERS FOR
YOU.

<[╘ONY] ┴.╘╧╠╠┼> ╬OW THAT YOU HAVE ENTERED THAT INSTRUCTION, YOU WILL SEE:

<[╘ONY] ┴.╘╧╠╠┼> ┴ $├003

<[╘ONY] ┴.╘╧╠╠┼> WITH A CURSOR.

<[╘ONY] ┴.╘╧╠╠┼> ╬OW THAT YOU ARE FINISHED TYPING IN THE PROGRAM, YOU WOULD
PRESS ╥┼╘╒╥╬ TO EXIT THE MINI-ASSEMBLER.

<[╘ONY] ┴.╘╧╠╠┼> ╬OW YOU ARE READY TO ACTUALLY RUN THE ═╠ PROGRAM TO SEE WHAT
IT DOES.  ┬EFORE YOU DO THAT THOUGH, YOU CAN DO WHAT IS CALLED "DISASSEMBLING"
THE PROGRAM, WHICH IS JUST A FANCY WAY OF SAYING THAT YOU WANT TO LIST THE ═╠
PROGRAM IN MEMORY.

<[╘ONY] ┴.╘╧╠╠┼> ╘YPE THE COMMAND:

<[╘ONY] ┴.╘╧╠╠┼> ─ $├000 $├002

<[╘ONY] ┴.╘╧╠╠┼> ╫HICH MEANS, "DISASSEBLE THE ═╠ PROGRAM FROM ADDRESS $├000 TO
$├002".  ╨RESS ╥┼╘╒╥╬ AND YOU WILL SEE:

<[╘ONY] ┴.╘╧╠╠┼> *├000 ┴9 10    ╠─┴ #$10 <[╘ONY] ┴.╘╧╠╠┼> *├002 00       ┬╥╦

<[╘ONY] ┴.╘╧╠╠┼> ╘HE HEX NUMBERS SHOWN TO THE LEFT OF THE MNEMONIC
INSTRUCTIONS ARE THE ACTUAL ═╠ INTRUCTION CODES THAT ARE STORED IN MEMORY.
╬OTICE THAT THE ═╠ PROGRAM ONLY TAKES UP THREE BYTES OF MEMORY.

<[╘ONY] ┴.╘╧╠╠┼> ┬EFORE WE RUN THE PROGRAM, WE SHOULD ALSO DO ONE OTHER THING.
╬OTICE THAT THE PROGRAM IS SUPPOSED TO ALTER THE ┴CCUMULATOR; WE NEED TO RESET
THE VALUE OF THE ACCUMULATOR BEFORE RUNNING THE PROGRAM SO THAT WE CAN SEE
WHAT THE PROGRAM DOES.  ─O THIS BYTE TYPING "╥" AND PRESSING ╥┼╘╒╥╬.

<[╘ONY] ┴.╘╧╠╠┼> ╘HIS WILL SHOW THE VALUES OF THE REGISTERS LIKE THIS:

<[╘ONY] ┴.╘╧╠╠┼>    ╨├  ┴╥ ╪┘ ┘╥ ╙╨ ╙╥ <[╘ONY] ┴.╘╧╠╠┼> ; ╪╪╪╪ ╪╪ ╪╪ ╪╪ ╪╪ ╪╪

<[╘ONY] ┴.╘╧╠╠┼> ╘HE VALUES THAT ARE PRINTED DON'T REALLY MATTER, BUT WE DO
WANT TO CHANGE ONE OF THEM.  ═OVE THE CURSOR TO THE FIRST DIGIT OF THE HEX
NUMBER BELOW THE ┴╥ HEADING.

<[╘ONY] ┴.╘╧╠╠┼> ╘YPE OVER THE NUMBER THERE AND PUT "00" INSTEAD.  ╘HE LINE
SHOULD LOOK LIKE THIS:

<[╘ONY] ┴.╘╧╠╠┼> ;╪╪╪╪ 00 ╪╪ ╪╪ ╪╪ ╪╪

<[╘ONY] ┴.╘╧╠╠┼> ╫HERE THE ONLY NUMBER YOU HAVE CHANGED IS THE SECOND NUMBER,
THE ACCUMULATOR.  ╘HEN PRESS ╥┼╘╒╥╬ TO CHANGE THE VALUE.

<[┼DDIE] ┼.┬╧╒╥─╧╬1> ╫HAT DO THE ABOVE LETTERS STAND FOR?

<[╘ONY] ┴.╘╧╠╠┼> ╧K, THEY ARE THE NAMES OF THE REGISTERS.   ╨ROGRAM ├OUNTER
(╨├), ┴CCUMULATOR (┴╥), ╪ REGISTER (╪╥), ┘ REGISTER (┘╥), ╙TACK ╨OINTER (╙╨),
╙TATUS ╥EGISTER (╙╥)

<[╘ONY] ┴.╘╧╠╠┼> ╬OW WE ARE READY TO RUN THE PROGRAM.  ╘YPE THE FOLLOWING:

<[╘ONY] ┴.╘╧╠╠┼> ╟ $├000

<[╘ONY] ┴.╘╧╠╠┼> AND PRESS ╥┼╘╒╥╬.

<[╘ONY] ┴.╘╧╠╠┼> ╔T WILL SEEM AT FIRST AS IF NOTHING REALLY HAPPENED, BUT THE
MONITOR WILL DISPLAY THE REGISTERS AGAIN LIKE THIS:

<[╘ONY] ┴.╘╧╠╠┼>   ╨├  ┴╥ ╪╥ ┘╥ ╙╨ ╙╥ <[╘ONY] ┴.╘╧╠╠┼> ;╪╪╪╪ 10 ╪╪ ╪╪ ╪╪ ╪╪

<[╘ONY] ┴.╘╧╠╠┼> ┘OU WILL SEE THAT THE VALUE OF THE ┴CCUMULATOR (┴╥) HAS
CHANGED TO HEXADECIMAL 10.  ╘HIS WHAT THE PROGRAM DID WITH THE ╠─┴ #$10
INSTRUCTION.

<[╘ONY] ┴.╘╧╠╠┼> ╬OW THAT WE HAVE DONE THIS SIMPLE PROGRAM, WE CAN TRY ONE
THAT DOES SOMETHING A LITTE MORE EVIDENT.

<[╘ONY] ┴.╘╧╠╠┼> ╫E CAN GO AHEAD AND PUT THE NEW PROGRAM IN PLACE OF THE OLD
ONE.  ╒SING THE MINI-ASSEMBLER TYPE THE FOLLOWING PROGRAM:

<[╘ONY] ┴.╘╧╠╠┼> ┴ $├000 ╠─┴ #$30 <[╘ONY] ┴.╘╧╠╠┼> ┴ $├002 ╙╘┴ $0400 <[╘ONY]
┴.╘╧╠╠┼> ┴ $├005 ┬╥╦

<[╘ONY] ┴.╘╧╠╠┼> ╬OW THAT THE PROGRAM IS TYPED IN, CLEAR THE SCREEN AND PRESS
╥┼╘╒╥╬ A COUPLE TIMES.

<[┼DDIE] ┼.┬╧╒╥─╧╬1> ╙EE YA ALL LATER

** <[┼DDIE] ┼.┬╧╒╥─╧╬1> HAS LEFT.

<[╘ONY] ┴.╘╧╠╠┼> ╘HEN TYPE "╟ $├000" AND PRESS ╥┼╘╒╥╬, BUT BE SURE TO BE
WATCHING THE UPPER LEFT CORNER OF THE SCREEN WHEN YOU ARE PRESSING ╥┼╘╒╥╬.

<[╘ONY] ┴.╘╧╠╠┼> ┘OU SHOULD SEE A "0" CHARACTER APPEAR IN THE UPPER LEFT
CORNER OF THE SCREEN WHEN YOU RUN THE PROGRAM.

<[╘ONY] ┴.╘╧╠╠┼> ╚ERE IS HOW THE PROGRAM WORKS:

<[╘ONY] ┴.╘╧╠╠┼> ╠─┴ #$30 LOADS THE ACCUMULATOR WITH THE HEX VALUE $30, WHICH
IS 48 IN DECIMAL.  ╘HIS IS THE NUMBER THAT THE COMPUTER USES TO REPRESENT THE
"0" CHARACTER ON THE SCREEN.  ╘HE NEXT INSTRUCTION, ╙╘┴ $0400, STORES THE
VALUE OF THE ACCUMULATOR ($30) IN THE FIRST LOCATION OF ╙CREEN ═EMORY.  ╙CREEN
MEMORY IS A RANGE OF ADDRESSES,

<[╘ONY] ┴.╘╧╠╠┼> $0400 TO $07╞╞, THAT IS THE COMPUTER'S INTERNAL
REPRESENTATION OF EVERY CHARACTER DISPLAYED ON THE SCREEN.  ╘O DISPLAY
DIFFERENT CHARACTERS, THE COMPUTER CHANGES SCREEN MEMORY IN A WAY THAT IS
USUALLY TRANSPARENT TO US. ╫HEN YOU CLEAR THE SCREEN THE COMPUTER IS ACTUALLY
FILLING SCREEN MEMORY WITH $20 BYTES, WHICH IS SIMPLY THE VALUE THAT
REPRESENTS THE "SPACE" CHARACTER.

<[╞RANK] ┬╒╞╞.╨╚╧╧╬> ╘IME IS ABOUT UP, ╘ONY.

<[╘ONY] ┴.╘╧╠╠┼> ┘OU ARE RIGHT...  ╔ DIDN'T EVEN NOTICE  HEHEHEHE.

<[╘ONY] ┴.╘╧╠╠┼> ╫ELP, IF THERE ARE ANY QUESTIONS ABOUT WHAT ╔ COVERED ╔'D BE
HAPPY TO ANSWER THEM NOW.

<[╞RANK] ┬╒╞╞.╨╚╧╧╬> ┘OU WANT US TO TRY WHAT WE'VE TALK ABOUT TONIGHT BEFORE
WE COME BACK NEXT WEEK?

<[╘ONY] ┴.╘╧╠╠┼> ┘ES.  TRY OUT THOSE SAMPLE PROGRAMS SO ╔ CAN FIND OUT WHAT
KIND OF TROUBLE YOU MIGHT HAVE ENCOUNTERED...

<[╘ONY] ┴.╘╧╠╠┼> ╔ WILL UPLOAD THE TRANSCRIPT OF THIS AS SOON AS ╔ CAN SO YOU
CAN ─╠ IT IF NECESSARY FOR REFERENCE, OR YOU CAN USE YOUR OWN BUFFER,

<[╘ONY] ┴.╘╧╠╠┼> EVERYTHING SHOULD WORK AS DESCRIBED FOR THE PROGRAMS THOUGH.

<[╞RANK] ┬╒╞╞.╨╚╧╧╬> ╧╦.  ╔'LL TRY IT THIS WEEK-END. :: ┬UFFER OFF ::