Specifications

EssentialsofCrestronProgramming
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TheInterlocksymbolwilllatchanoutputhighontherisingedgeofitscorresponding
input.Inaddition,anyotheroutputsignalthatwaspreviouslyhighwillbelatchedoff.
Thusthissymbolwillhaveatmostoneoutputhighatanygiventime.Thispropertyis
calledbreakbeforemake.Inesse
nce,thissymbolwillrememberwhichinputwaslast
drivenhigh,makingitveryhandywhentheuserhastoselectfromanumberofchoices.
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IntheVirtualPresentationRoomprogramthissignifiesthatwhentheuserpressesthe
ScreenUpbutton,thiswilltriggertheScreenUpinputoftheinterlocksymbol,latching
theScreen_Up_FBoutputhigh.Sincethisoutputisthedrivingsourceofthe<fb21>
inputofthetouchpanel,thebuttonwillshowactivefeedbackforaslongastheScreen
Upinterlockislatchedhi
gh.
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Similarly,whentheuserpressestheScreenDownbutton,thi
swilltriggertheScreen
DowninputoftheInterlocksymbol,latchingthecorrespondingoutputhigh,and
activatingthecorrespondingbuttonfeedback.
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NotethatinthisexampletheoutputsignalsoftheInterlocksymbolarebeingusedfor
feedbackonly,andarenotbeingroutedtotheC2Icardtoopenandclosetherelays.
ThisisbecausetheoutputsoftheInterlockarelatched,anditisgenerallyconsidered
poorprogrammingtodrivemomentaryfunctions(suchasarelaycommand)witha
latchingsignal,eventhoughinsomecasesitmaywork corr
ectly.Sincewehave
momentarysignalsalreadyontheinputsideofthesymbol,itis“cleaner”tousetheseto
drivetherelays.
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WehaveseenhowtheIn
terlockandTogglesymbolsareevent‐driven; thatis,whenan
event(arising‐edgetransition,forexample)occursthesymboldrivesitsoutputsignals
totheappropriatelevels.Sometimesthisisnotsufficient,however,andyouneedto
controlwhenthingswillhappen.Inthecaseofrelaycontrols,thecontrolledscreenne
eds
tobeassertedforaperiodoftime,asspecifiedbythemanufacturer.TheOneShot
symbolallowsthistypeoftime‐basedcontrol.
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