TIFILES‚’þÊSÊSÊSÊSÊSÊSÊSÊSÊSÊSÊSÊSÊSÊSÊSÊSÊSÊSÊSÊSÊSÊSÊSÊSÊSÊSÊSÊSÊSÊSÊSÊSÊSÊSÊSÊSÊSÊSÊSÊSÊSÊSÊSÊSÊSÊSÊSÊSÊSÊSÊSÊSÊSÊSÊSÊSþý;2749Œl20Œr20Œm20Œp10Œs2ˆPOKEV€AND€THE€MINI-MEMORY‚‚ƒOne€of€the€most€powerful€aspects€ofthe€TI€Mini-Memory€Module€is€its€abilityto€access€VDP€RAM€directly€through€the€€function.€Since€the€video€processor€is€directly€accessed,€the€monitor€scÿþýreen,€which€is€controlled€by€the€VDP,€is€also€directly€accessed.€The€code€entries€forthe€equivalent€of€Extended€BASIC's€€and€€functions€takea€little€getting€used€to,€but€they€are€actually€easier€to€enter,€once€you€master€the€conversioÿþýn€factors;€and€of€course€they€are€much€faster€than€anything€available€in€console€BASIC.€In€fact,€using€€to€control€color€is€even€faster€than€anything€in€Extended€BASIC.‚ƒHere€are€two€possible€approaches€to€using€€to€display€a€string€anywheÿþýre€on€the€screen.€The€first€method€is€the€simplest€and€the€fastest.€First,€you€must€determine€the€starting€position€of€your€text€by€row€[R]€and€column€[C].€To€convert€these€values€to€the€proper€address€in€VDP€RAM€you€apply€this€formula:€PADDR=((R-1)*32)ÿþý+C+1.€VDP€RAM€reads€the€screen€left€to€right€and€numbers€each€position€consecutively,€so€the€first€part€of€the€formula€adds€32€places€to€the€address€for€each€complete€row€and€then€adds€in€the€column€number,€correcting€for€the€fact€that€print€column€#1€iÿþýs€screen€column€#3.€Once€you've€determined€the€screen€address€in€VDP€RAM,€you€simply€'poke'€the€codes€for€each€character€in€your€string€into€the€VDP€RAM€in€one€statement:€€instead€of€,€but€it€would€run€about€16%€more€slowly.€Of€course€we're€not€talking€about€blinding€speed€in€any€case,€but€16%€is€an€improvement.€Another€application€wherÿþýe€both€speed€and€convenience€would€show€up€would€be€updating€a€short€timing€or€scoring€display€on€agame€screen.Œl35‚‚100€CALL€CLEAR‚110€CALL€POKEV(393,179,163,175,178,‚‰‰‰‰165,128,157)‚120€FOR€X=1€TO€50‚130€RANDOMIZE‚140€SCORE=(99*RND)‚150€IF€SCORE>9€THÿþýEN€180‚160€CALL€POKEV(401,ASC(STR$(SCORE))+96)‚170€GOTO€190‚180€CALL€POKEV(401,ASC(STR$(SCORE))+96,‚‰‰‰‰ASC(SEG$(STR$(SCORE),2,1))+96)‚190€CALL€SOUND(50,2200,0)‚200€NEXT€XŒl20‚ƒThis€program€is€slower€than€it€has€to€be€because€it€is€generating€each€randoÿþým€score€before€it€is€displayed€and€pausing€during€the€execution€of€the€command.‚ƒAs€I€hinted€above,€you€can€also€use€€to€make€direct€alterations€to€the€color€tables€located€in€VDP€RAM.€Since€one€integer€value€at€a€single€address€in€the€colÿþýor€table€sets€both€the€foreground€and€background€colors,€you€need€to€enter€only€two€values€to€fully€define€any€one€color€set,€as€opposed€to€three€values€in€the€€subroutine,€and€€executes€much€faster€than€.‚ƒProbably€the€most€useful€ÿþýapplication€of€using€€to€define€and€redefine€color€sets€is€to€make€things€flash.€Since€€executes€much€more€quickly€than€,€you€can€make€things€flash€more€rapidly;€and€since€you€can€alter€several€color€sets€virtually€instantaneously,€ÿþýyou€can€flash€groups€of€characters€in€more€than€one€color€set...a€line€of€text,€for€example.€Here's€a€simple€program€to€demonstrate€flashing€text.Œl35‚‚100€BKG=0‚110€FGD=1‚120€CALL€CLEAR‚130€PRINT€TAB(3);"THIS€DEMONSTRATES€COLOR"‚140€PRINT€TAB(3);"FLASHÿþýING€USING€"‚150€PRINT€TAB(3);"AND€THE€MINI-MEM€MODULE"‚160€PRINT€::::::::‚170€FOR€I=1€TO€50‚180€CC=(16*BKD)+FGD‚190€CALL€POKEV(788,CC,CC,CC,CC)‚200€CC=(16*FGD)+BKD‚210€CALL€POKEV(788,CC,CC,CC,CC)‚220€NEXT€IŒl20€‚ƒThe€necessary€addresses€and€valueÿþýs€are€very€easy€to€calculate.€In€BASIC,€the€color€table€for€character€set€one€is€located€at€VDP€RAM€address€784,€and€the€successive€addresses€control€each€successive€set.€Each€address€holds€a€two-place€hexidecimal€value,€the€right-hand€hex€digit€is€the€ÿþýbackground€color€code,€the€left-hand€digit€is€the€foreground.€These€codes€are€the€TI€BASIC€color€codes€minus€one.€To€convert€the€two-place€hexidecimal€code€to€decimal€you€multiply€the€foreground€code€by€16€and€then€add€the€background€code,€yielding€a€deÿþýcimal€value€from€0€to€255.€In€the€program,€line€180€reverses€that€calculation€to€reverse€the€colors€of€the€text,€and€line€200€restores€the€normal€values.€Lines€190€and€210€push€these€values€into€the€VDP€RAM€color€table€starting€at€788,€which€is€the€addrÿþýess€of€character€set€5,€and€into€the€next€three€successive€addresses€and€character€sets.€These€four€sets€include€all€the€upper-case€characters.€You€can€see€how€quickly€the€color€codes€of€all€four€sets€are€altered.‚ƒOf€course,€you€could€makes€the€text€flÿþýash€any€color€combination€you€want.€Try€adding€these€lines€to€that€program:Œl35‚‚230€CALL€CLEAR‚240€PRINT€"ENTER€TWO€INTEGER€VALUES"‚250€PRINT€"BETWEEN€0€AND€15.€REMEMBEŒ"‚260€PRINT€"TO€SUBTRACT€ONE€FROM€THE"‚270€PRINT€"VALUES€IN€TI€BASIC..."‚280€PRINT‚ÿþý290€INPUT€"FOREGROUND?€":FGD‚300€INPUT€"BACKGROUND?€":BKD‚310€GOTO€170Œl20‚ƒAgain,€equivalent€statements€exist€in€Extended€BASIC,€since€you€can€enter€a€long€parameter€list€in€a€€statement€and€alter€several€color€sets€at€once,€but€the€execution€ofÿþý€such€a€command€isn't€as€fast,€so€the€sequential€changes€to€the€several€color€sets€is€quite€perceptable€and€destroys€the€crisp€and€rapid€flash€effect€of€.€If€you€want€to€make€the€comparison€for€yourself,€be€sure€to€alter€this€program€to€take€out€ÿþýlines€180€and€200€which€execute€between€the€flashes€and€slow€the€program€down€considerably!‚ƒRemember,€BASIC€and€Extended€BASIC€functions€like€,€€and€€are€actually€whole€machine€language€routines€which€result€in€an€alteration€oÿ‘f€the€VDP€RAM.€€makes€the€same€alterations€directly;€that's€where€it€gets€its€speed.‚„Richard€G.€Minutillo„August€15,€1983ŒlŒrŒpŒmŒs124ˆÿOLOR>,€€and€€are€actually€whole€machine€language€routines€which€result€in€an€alteration€oÿ