оK, SO YOU WANNA KNOW HOW TO ACCESS THE MEMORY IN THE GEOрам FROM YOUR OWN басиц PROGRAMS. вELL THEN, HERE'S THE SKINNY, IN AS SIMPLE TERMS AS и CAN COME UP WITH. паге тHE FIRST THING TO UNDERSTAND IS WHAT WE MEAN BY THE WORD паге. фOR OUR PURPOSES, A паге IS ANY 256 BYTES OF CONTIGUOUS MEMORY (THAT IS, ANY 256 BYTES 'IN A ROW'.) фOR EXAMPLE, MEMORY LOCATIONS 0 THROUGH 255 ARE THE FIRST паге IN THE COMPUTER, WHILE LOCATIONS 256 THROUGH 511 ARE THE NEXT паге, ETC. тHE ц= 64 CONTAINS 256 пагеS OF MEMORY SPACE. тHE GEOрам CAN STORE UP TO 2048 пагеS OF DATA (I.E., 524,288 BYTES). (ыOU MIGHT NOTICE THAT A паге IS THE SAME SIZE AS A 'BLOCK' OR 'SECTOR' ON A DISK. аLSO, SINCE FOUR пагеS EQUALS ONE кILOBYTE, THE 512к OF THE GEOрам TIMES 4 EQUALS 2048 PAGES, AS STATED ABOVE. тHIS ISN'T IMPORTANT TO OUR DISCUSSION, BUT IT MIGHT HELP YOU UNDERSTAND THE CONCEPT OF паге.) оK... THE GEOрам USES 258 BYTES OF MEMORY SPACE IN THE COMPUTER TO HELP PASS INFORMATION BACK AND FORTH TO COMPUTER. тHE пAGE сELECT рEGISTERS тWO OF THE 258 BYTES ARE CALLED THE пAGE сELECT рEGISTERS. 57342 IS THE лOW пAGE сELECT рEGISTER AND 57343 IS THE хIGH пAGE сELECT рEGISTER. (тHE OTHER 256 BYTES ARE CALLED THE GEOрам вINDOW, MORE ABOUT THAT LATER.) оNLY ONE паге OF THE 2048 пагеS IN THE GEOрам MAY BE ACCESSED AT ANY ONE TIME. тO TELL THE GEOрам WHICH паге YOU WANT TO WORK ON, YOU SIMPLY поке VALUES INTO THE пAGE сELECT рEGISTERS. тHE лOW пAGE сELECT рEGISTER (57342) IS покеD WITH A VALUE FROM 0 THROUGH 63, WHILE THE хIGH пAGE сELECT рEGISTER (57343) IS покеD WITH A VALUE FROM 0 THROUGH 31. сINCE THE лOW пAGE сELECT рEGISTER CAN BE покеD WITH 64 DIFFERENT VALUES, AND THE хIGH пAGE сELECT рEGISTER CAN BE покеD WITH 32 DIFFERENT VALUES, WE CAN ACCESS ALL 2048 пагеS OF THE GEOрам. (32*64=2048) фOR EXAMPLE, TO ACCESS THE FIRST паге IN THE GEOрам, WE поке 57342,0 AND поке 57343,0. аS SOON AS VALUES ARE покеD TO THE пAGE сELECT рEGISTERS, THE GEOрам DISPLAYS ITS CORRESPONDING паге IN THE GEOрам WINDOW. тHE GEOрам вINDOW мEMORY LOCATIONS 56832 THROUGH 57087 IN THE COMPUTER ARE CALLED THE GEOрам вINDOW. тO STORE DATA IN THE GEOрам, JUST поке THE DATA TO THESE LOCATIONS. тO RETRIEVE IT, пеек THE SAME LOCATIONS. вHEN YOU поке NEW VALUES TO THE пAGE сELECT рEGISTERS, THE GEOрам AUTOMATICALLY SAVES THE DATA FROM THE вINDOW TO THE PROPER паге OF ITS MEMORY, AND DISPLAYS THE DATA OF THE NEW паге IN THE вINDOW. тHE WORD вINDOW IS A GOOD DESCRIPTION OF THE MEMORY LOCATIONS 56832 THROUGH 57087, SINCE THAT MEMORY SPACE IN THE COMPUTER ACTS LIKE A 'WINDOW' THROUGH WHICH YOU CAN LOOK AT THE пагеS OF MEMORY IN THE GEOрам, ONE AT A TIME. еXAMPLE пROGRAM хERE IS A USELESS, DIRTY LITTLE PROGRAM TO GIVE YOU AN IDEA OF HOW THE GEOрам MAY BE ACCESSED. лET'S SAY THAT WE WANT TO FILL THE GEOрам WITH KEYPRESSES. дON'T TRY TO ACTUALLY USE THIS PROGRAM, UNLESS YOU PLAN TO SPEND MANY HOURS PRESSING 524,288 KEYS! тHIS IS JUST AN EXAMPLE OF HOW THE рEGISTERS AND THE вINDOW MAY BE USED. иF SOME OF THE PREVIOUS INFORMATION ISN'T CLEAR YET, PERHAPS STUDYING THIS PROGRAM WILL HELP: 10 хп=57342: рем хIGH пAGE сELECT рEGISTER 20 лп=57343: рем лOW пAGE сELECT рEGISTER 30 ь=0: рем STARTING VALUE FOR хп 40 ы=0: рем STARTING VALUE FOR лп 50 поке хп,ь: рем POKE VALUE INTO хп 60 поке лп,ы: рем POKE VALUE INTO лп 70 фор й=0 то 255: рем LOOP 256 TIMES 80 гет а$: иф а$="" тхен 80: рем GET A KEYPRESS 90 к=асц(а$): рем CHANGE KEYPRESS TO VALUE 100 поке 56832+й,к: рем POKE IT TO GEOрам вINDOW 110 неьт й: рем GET ANOTHER KEYPRESS AND POKE IT 120 ы=ы+1: рем INCREMENT THE лOW рEGISTER 130 иф ы<64 тхен 60: рем GET THE NEXT PAGE 140 ы=0: рем лп REACHED 64 SO RESET TO 0... 150 ь=ь+1: рем ...AND INCREMENT THE хIGH рEGISTER 160 иф ь<32 тхен 50: рем GEOрам NOT FULL YET 170 енд: рем GEOрам IS FULL OF KEYPRESSES (иF YOU WISH TO ACTUALLY TRY THE PROGRAM ABOVE, LOWER THE MAXIMUM VALUES OF ь AND ы IN LINES 130 AND 160, SO THAT YOU ONLY STORE A FEW THOUSAND KEYPRESSES! тHEN рун THE PROGRAM AND SPEND SOME TIME PRESSING KEYS UNTIL YOU GET THE реады PROMPT WHEN THE PROGRAM ENDS.) тO RETRIEVE THE KEYPRESSES STORED BY THE ABOVE PROGRAM AND PRINT THEM TO THE SCREEN, WE COULD рун THE FOLLOWING PROGRAM: 10 хп=57342: лп=57343 20 ь=0 30 ы=0 40 поке хп,ь 50 поке лп,ы 60 фор й=0 то 255 70 к=пеек(56832+й) 80 принт цхр$(к); 90 неьт й 100 ы=ы+1 110 иф ы<64 тхен 50 120 ы=0 130 ь=ь+1 140 иф ь<32 тхен 40 150 енд (иF YOU TRY THIS PROGRAM, LOWER THE MAXIMUM VALUES IN LINES 110 AND 140 TO MATCH THOSE YOU USED IN THE FIRST PROGRAM!) бY STUDYING THE EXAMPLES ABOVE, YOU SHOULD BE ABLE TO REACH AN UNDERSTANDING OF HOW THE пAGE сELECT рEGISTERS AND THE GEOрам вINDOW CAN BE USED TO ACCESS THE MEMORY SPACE IN THE GEOрам. вITH A LITTLE CREATIVITY, YOU MIGHT FIND A USE FOR THIS IN YOUR OWN басиц PROGRAMS. а фEW нOTES: тHE DATA NEED NOT COME FROM KEYPRESSES, IT COULD BE READ IN FROM A сея FILE ON DISK, OR GENERATED IN ANY NUMBER OF OTHER WAYS. иT IS NOT NECESSARY TO COMPLETELY FILL EVERY BYTE IN A PAGE. фOR EXAMPLE, THE FIRST BYTE IN EACH PAGE COULD BE USED TO HOLD A VALUE CORRESPONDING TO THE NUMBER OF BYTES STORED IN THAT PAGE. (тHIS MIGHT BE USEFUL FOR SOMETHING LIKE STORING A DATABASE OF UP TO 2048 RECORDS OF LESS THAN 256 BYTES EACH.) тHE пAGE сELECT рEGISTERS CANNOT BE пеекED, THEY CAN ONLY BE покеD. сO YOU MUST KEEP TRACK OF THE LAST VALUE покеD. уSING A VARIABLE (AS и DID WITH ь AND ы IN THE EXAMPLE PROGRAMS) IS PERHAPS THE EASIEST WAY. иF YOU NEED ANY FURTHER HELP WITH THIS INFORMATION, OR WISH TO MAKE ANY COMMENTS OR SUGGESTIONS, FEEL FREE TO SEND EMAIL TO мINK.