导致sV
C
(seeFigure5)torise一个sthecapacitordischarges.
提供dthatthesignalconditionismaintained(est仍然是
高)forthevalidationperiod(t
GTP
),V
C
reachesthe门槛
(v
TSt
)ofthesteeringlogictoregisterthetone一双,latching它的
corresponding4-bitcode(seeTable2)intothereceivedat一个reg
-
ister.
一个tthispointtheStGToutputis活动d一个d驱动sV
C
toV
DD
.
StGTcontinuestodrivehigh一个slong一个sESt仍然是s高.
最终,afterashortdelaytoallowtheoutputlatchtosettle,这
delayedsteeringoutputflaggoes高,signalingthatareceived
tonepairhasbeen注册.Itispossibletomonitorthe状态
ofthedelayedsteeringflagbycheckingtheappropriatebitin这
status寄存器.Ifinterruptmodehasbeen选择,theIRQ
/cp
pinwillpulllowwhenthedelayedsteeringflagis起作用的.
The内容softheoutputlatchare更新don一个nactivede
-
layedsteering转变.Thisdat一个ispresentedtothe4-位
bidirectionaldat一个buswhenthereceivedat一个registeris读.
Thesteeringcircuit工作sinreversetovalidatetheinterdigit
pausebetween信号.因此,一个swell一个srejecting信号stoo
shorttobeconsidered有效的,thereceiverwilltoleratesignal在
-
terruptions(落后)至oshorttobeconsideredavalidpause.
This能力,togetherwiththeabilitytoselectthesteering
time常量sexternally,准许sthedesignertotailorperfor
-
mancetomeetawidevarietyofsystem(所需的)东西.
GuardTime调整:
Thesimplesteeringcircuit显示n在
Figure5isadequateformost产品.Component值
arechosenaccordingtotheformula:
t
REC
=t
DP
+t
GTP
T
ID
=t
DA
+t
GTA
Thevalueoft
DP
isadeviceparameter一个dt
REC
isthe最小
signaldurationtobe认识dbythe接受者.一个valueforC1
of0.1
µ
Fisrecommendedformost产品,leavingR1至
beselectedbythe设计者.Differentsteeringarrangements
毫安ybe使用dtoselectindependentlytheguard时间sfor声调
present(t
GTP
)一个dtoneabsent(t
GTA
).This毫安ybenecessary至
meetsystem规格sthatplacebothaccept一个dreject
限制sonbothtoneduration一个dinterdigitpause.Guardtimead
-
justmentalso准许sthedesignertotailorsystem参数
such一个stalkoff一个dnoise免除.Increasingt
REC
改进
talkoffperformancesinceit减少stheprobabilitythattones
simulatedbyspeechwillmaintainsignalconditionlong足够的
tobe注册.Alternatively,一个relativelyshortt
REC
witha长
t
做
wouldbeappropriateforextremelynoisy环境
wherefastacquisitiontime一个dimmunitytotone落后s是
必需的.Designinformationforguardtimeadjustmentis显示
inFigure6.
call progress 过滤
一个callprogress(cp)modecanbe选择,allowingthedetec
-
tionofvarious声调sthatidentifytheprogressofatelephonecall
onthe网络.Thecallprogresstoneinput一个dDTMFinput是
一般;不管怎样,callprogress声调scanonlybe发现
whentheCPmodehasbeen选择.DTMF信号scannot是
Page3
m-8880
40-406-00012, rev. g www.clare.com
F
低
F
高
数字D3D2D1D0
697120910001
697133620010
697147730011
770120940100
770133650101
770147760110
852120970111
852133681000
852147791001
941133601010
9411209
1011
9411477#1100
6971633一个1101
7701633B1110
8521633C1111
9411633D0000
0 = 逻辑 低, 1 = 逻辑 高
表格 2 声调 encoding/解码
图示 5 基本 steering 电路
图示 6 守卫 时间 调整
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