ÿðáãëþHOW XL2 WORKS (PROGRAMMING STUFF)››~uses two areas in RAM. The low memory portion, up to 99 byte~/length, provid~Mhe entry and exit points for all func~Os. 49 more~Oare~‘d~*~Hdisplay list~O~
ne which also must be~‘ma~Å››With SpartaDOS 3.2+ this code replace~in ~$~Tsup~ó~Íkeyboard buffer. ~W3.2g~Mis a tight fit leaving seven~Ùto spare; w~<other vers~D~ere's 51 un~E ~I^~a~D› after~EÒgets do~D~Mit~E¯re~‰yet~FQroom~EGexpan~h~.out bump~¡MEMLO under~G% a~ò itself~`now~¤.››U~;~D], patch~»to~EP~DÓmade~Dmodify~bRT8~Fwto pr~D*t it from enabl~¡a cartridg~Hìis~F›~D$to~Dñoff~…~Dbteal~†7ay-of-the-week~j~Dits own~„e. Fur~Eˆhook~†|~©al~„üacces~E¼~Tbuilt-in,~¼"set"~y"g~
~‹ÓAll of~4se~I~^~Gð dependant s~[installa~A h~D„o search through~EKto fi~ëhe correct addres~ÄÄ~E~t~lsaved~†A~Dta~ÆXby~…Bfo~á~Fcsystem swap.››~Äøonly~‡£~ÅLmemory~Ais~†u~Wformatt~D‹ime/date~I~G°u~š~,prin~„À~‡Q~Åàemporary storage~Ã last two~Çon p~zero~„¢a po~N. Since~4user's~`~G may well~„*~G$4000-$7FFF range, I saw n~Døternative~isome~Äg~Fdeci~†write~…rogram~ê~†-~î~†p~„ÌBW-DOS,~%would not permit~¶~‡, non-exist~Äkey~Ë. U~
$~Kf float~DÄ~E RAM~N*hav~Dxesen~D¤n~Äioblem (I'm~†dea~Åi~EÓan~Ä¶errupt here).››When copy~'OS~f~Ä!n extra bank, most~Hmers~EÒe $C~EkC~Dkat~Hz4~nd $D8~~5~~D˜;~…¥do~GNsame. This leav~…ì un~…2k~<~Z57FF~Gj~„¨~Ä~A~…Æ~F”or~\lives~Te ~Äê~Ö~ simply enabl~~appropri~„Þ~
ô~ÁJMP's or JSR'~Å¶~Dntry~G”~…si~Åþa. Upo~‡mple~Ä#,~œreturn~G~”~Çvto re~~,~¬~}~I¬s.››IMMEDIATE VERTICAL BLANK››Dur~D»~EHt~„1 vbl~E¶~…ªartridg~tus~D9checked. If vibra~ÅÑor heavy~…œ~„W~„í~…dinadver~„¹~I<d a~\that was ~âed off,~Fäis~Fjit ag~ßbef~„;~œOS finds out it~Dkn~ûsh~ÄHn't~Ä×(lockup time)~‡'is m~F~EïE~D›han XL's beca~Çvphysical design.››Next~{jiffy cou~De~Odecrem~ÆJand, if~ÅB~Äj~Ëexit~E½~»~Hn~DÜ. Otherwis~Ú~Y~Ä t~760 (NTSC)~Dj50 (PAL)~ï~2~æ~0in~
‰by a second~H8~†~
….››DEFERRED~‘Firs~ícon~D¼~DDOSINI~‹~Lensure~D£is~õ~…Ý~…Vo p~æ7~…,~!~Fretakes~P~J–required~Eštwo-part~&~Ç·~F~†every~D× you go~ØDUP menu. Af~DF~„^~†Îfollow~šfunc~„·s (a-d) occur only~Dº~,display line~›on:››a.~st~Æmts add~„ö~ÄÕSDLSTL,~ÄØ verifi~† adjus~D›if~
ìto match~[~ÆJoff~Èqo~TD~Š;››b. once each minut~†5~±, from day-of-the-week~H!e~…¡s upda~‡± step c.~skipped;››c~ï~†Cs por~Æë~V"~O~žper~8;~`››d~Dæe typ~Å]~=(drive~ôx-y)~ŒZ~–~	¢~Š.››~HHelp key~2a swap~P~handl~„oggl~¥execu~G‚applicable~… nei~Ä†~[~ˆ! was called,~Fë~ý~^~…~†Ù~‹s~…¿~-~ns any repeat~o custom~E~i. When~\it completel~Jlaces~ÇÇ ome.››E~ÄÜis made via low memory~DúXITVBV. No attemp~
-~Ä¨~Ä[rve~ªdefer~„›vertical blank rout~Dí~-nt w~²~÷~Ä¾nst~E'.››SYSTEM SWAP››First~&dis~þs NMI's~DÕ~±possi~D~E7~~’interrupt~already~Ä`prog~Ålwith~Wstrou~„%sults. Next, aft~„‡av~Äóseveral curr~½values (stack po~p, etc.)~FÍexchang~GhRAM at $C000-$CFFF~extra~	4~4FFF~…ðn~ã~
Ha pag~Å it~D3tern~“ode~M~e~…Bjump~€r~E§get out~Èƒextended~8dd~Er~l.››From~hnew loca~„g~‡§~‡L~Ú~Æ2f~„J~Hby~²~D7$D8~Ò~ï$5~7~âIt~An~O*low~Äthree main bank~G­~or~½~bef~return~z~„~¾ormal~	Þi~Æ$four~F}~J~H~Ev~Ff~IHis ag~ˆ~§d~Œe~Gde so~previ~„Ksystem~<sto~Äcorrectl~…‚~Kõnd~È~† ~„Å~Jnext~E[~D‹ollow~Õ~Gp, a number~Dzvari~Æ~O~ë~re adjusted~Daccommodate~dw~©pri~yo exit~Éÿ~¢~Ëü~D~Eîproc~DNtak~gb~„Ttwo seconds,~„which amoun~Eç clock~ébump~ÅéKEYBOARD INTERRUPT››~dkey handler~EBimila~ž~Hone~HÇOS~J‹addi~„£~D~E“to check~ES~Dexecute any~Etkey~F2~?removal~	>support~Hu1200XL func~e~	<play~%~ˆPORTB.~FÑgnores KEYDIS.~Ùe~£ng~	Gs oper~Ddi~‡on screen~E}us~/valu~Dhl~†#set~Da~F~D–is~D'w~Åægood references~Ä¬~E/(Mapping... or~EËC~ÇÇ...). How often have you s~‡programs calcul~­an~ÉPo~F‰~³by~E‡~G4~ËtSAVMSC~D“COLCRS plus 40 times ROWCRS? Why?~›~	_f~†;urso~…~Hin OLDADR, c~ÄÌesy~-O~Hnkeyboard interrupt~Iîst~Äã~„³vertical blank both save,~,~ïr re~ÅÅ,~1byte~øp~Czero~ˆër~ÄReded~…rin~FÔ~Ì~D| T~Ä%ubroutines~‡æ~“~Dv~t~n as~Ž~	¾s us~,m~¾~~Špossible because:››a.~2~Wall other~DÞls~ÅíL2, except v~E, disa~W~IRQ'~†üNMI's s~Æ—~,~†inhibited until exit from~Š~G;~K››b~¨~Ä;~O“~Æets~!~
Àfla~DR~Scannot,~)ref~E³~
0~¥bu~ÿy~Ë will be~„ècessed~Dysoon~~K|~Dß~„å~D	d~È€RTI~
Ú~].››I~D1covered,~Ä˜n work~Äon~Fathat~„8~Gý6502~ä automa~Ely~Ban~º, it does not appear~DÁdo~D“~'~D¡~E"~H~9~D'~Œ~' with often unpleasant~„Œults.››LOW RAM CODING››To minimize low memory usage, maximum~…±of~Ç~…¡mad~ß~æmai~Jarea. A~D‹u~M«~Eþe~­~F~6program at one comm~Ä‘oint~Éa valu~	kX regis~ÄÌ~Æ¬is transferred~D6~ÅWtack~…Úpul~Dæin~~Á. F~Gë~DLsuc~„0ive branche~†$~ãdepend~DBon~	=~E~#u~‡ffollows:››  ~ U~DA   X=› sv.bdizc› .1.1 Reset  $05› .1..~Keyon   45› 1~. Gettd   C4› 1~S~8~~)1~)6 RT8 present~51~5~ ~’1. Fm~06~	’. On/off  44 TD line~Â.~­irq  04››~Ä»first~KAf~D¤entry~D*› BCC TD?› BVC XRESET›so, if both~
:fail you have~DÑbe~„~D½~…Cto handle Sparta's KEY~…;and.~Ž~*at~r is› BPL FMT~	SETRT8› BEQ G~~„.if a~„º~Œ,~~Dî~†a VGETTD ~ÄÖ f~„Y~™ us~Ä~3jiffy cou~„ÿ (no~Lƒ). Down~_~£ similar checks determine~ ~‚aller~„üa key IRQ, a t/d~E¤ o~E·, or return~Ä»a formatt~Ä'ime/date~G/disadvant~„³~Åk~Äãethod~fbit~Dlost~=~Å\space~V~E5~™~H9. ~V~S~Äóat a ~Dle low memory JSR~È·main~F_can~Dø~Åƒwithout each rout~ãhav~E]o~Fwa sub~to ~Ä^PORTB~©i~Dwrupts~ano~Äû~(restore~~m~Äâexit--~Nstantial s~kwhere it~FÇs:~D°Memlo~ívblank~ê~G¾ly~‡"d~Â~G¹rry flag~IÕ~ˆ#proces~…2~¤~‰ points.››A BYTE SAVING CHEAT››I'v~Eºcover~DÕ~Dbit~ƒunne~Nary~E#ontrol NMI's~‹—traditional manner. i.e. Instead of›  LDA #$00  ~„Q~$E0›  STA~TEN~
›~Ä/~DÀget away~ÿ›  INC~"~HDE~~†„reason~¾~%~…xwrite-only regist~£If~Å“r~¢~,~Ç£lways~w value~„³$FF no ~…ùr w~D$~-stuff~„o it. S~†effec~…ê~­~„¶o~ƒ zero~it while~¾~s $FE~ch enables~Å~Fmas ~¾~Eohree high~ÄPs~”~„?is~E¶seful~…¿ave by~]but no~Æv; ei~…º~Ç›require~„sx mach~„þcycl~Ä‚So, i~F*h~Oa known, suit~§~G$in a~I], ST(A/X/Y)~G‡wil~Åe two~	]~D±INC/~Dtric~…ùalso~ßly~GJive~„'re juggl~„|~Æšbetween OS ROM~…öRAM~ñ~FÐ~¶to keep~Ä:~Frack~D¡~DQ~H~Ç.››PROGRAMM~Ä#WITHOUT A~„˜CK››When~Gùart swapp~‹memory aroun~ÈCncludes page one~program~…Öout benefi~…5a~^ck. Onc~Dq~f~Dent~Ä¢, XL2 makes~„“us~…¡~É~7 until~…<~–for~new system has b~D6~Âed~†Ãpla~q~Â~Npoi~w~
2correctly set from~.~†~Dâd~qat~n.››L~GoJSR~Êovercom~…6~k~ârout~„zby us~DU~…i condition~ÅG~„ževe~Æ‚migh~D: called a "rela~…0sub~Q"~Obranch~„wFortunately,~Æ±xtended~IÈddress range~†”l posi~[o a~Æ€sign (or "N") flag indica~Äs~„¯ve ~èto~hnd~Dit. Similar~‚w~‡U~.passe~F€last~‡=f main~ž~³zero~r~Å[be~D~ÆR~HI~Eƒexch~Æs~6~Ocod~Ø, s~
‡~Ä¿~Q=~E~H; o~Dmple~D‘ ba~¬o~FÄcar~„llag.››THE SOURCE CODE››I~Ýmad~Q~DBur~„jvailabl~…unnumb~„á ASCII~„Fm~…Kexamina~s~Ä/ a word~ÄCcessor~…³easy~„-vers~*to non-MAC/65~Mat (ve~¥ew macros are employed). It's well-comm~Äqd (it~…þto~Df~‘~FÑmodify things af~Ä&several months away~Æ#it)~D~D(~D{~Å"ime, date,~Ákey func~†ì~…uways present~È,~Æýin~Dk~„Øarea. W~D¨is mis~„î,~G*ny DOS othe~Å”n Sparta,~ú~…gow RAM ent~„ú~DJxit~Æøs~…Qr~Åno reaso~…« cannot ac~D‚ s~„äof~Pse~Å~û~|FMS~ÄÚ~FÌ~·~‹~E~zwrit~your ~ÄýCOMs~G8set~$get~E;~ˆçs, under most~íwould require~®to: sav~ñcontents~±DOSVEC,~„ñstitut~ˆ~Éÿ~E~13 by~ÄÔbe~D/a desi~„ªsix-~ buffer, call~f~Ôt~ÄÞrestore~p. If~˜want~„K~Dz~DD~…L lik~ª~ÄŸensure Break~D…dis~Ä0d~Zat~FGystem will reboot if Re~D3i~†A~Ä©bef~
„~~–d. I~„\is case it~GCbe~ÄVier jus~©cop~„òe clock value~Fÿw~„(.››MODIFYING~„©››Currently,~Do2k~ËôRAM,~…Îuses 2048~Geso~¿~L ~ÇkXL2,~'ll h~EÏo manufact~D'~…‡space~…¸ best b~F~µkeyboard handler--~Ødecide w~DOfea~Ks~sacrific~FÑrip~Nm out, ta~Å…c~ÆOat~9remov~.y~‡þdepend~O~„. A~G¹ame~…Í,~3~§~Š?~‡æ~‰”~ÅS~&file STOW.M65. Likely~Ä˜dida~DGfor~Val~Éí~Ådefaul~ÆN~FÈset~…è~þ.››H~*fun~G|~XL2~‰ºd~„me up with~ëinte~„S~,~6ications or idea~”~D¦, I'd~‡éo hear abou~Em. You~Ê catch me o~„ e USF~LIAN~by mail~…y~„Fr group (GCACE).›››jkp›16 Feb 96›