detectediftheCPmodehasbeenselected(seeTable3).图
-
ure7表明stheusefuldetectbandwidthofthecallprogress
过滤.Frequenciespresentedtotheinput(在+一个d在-)that是
withinthe“accept”bandwidth限制softhefilterarehard-限制
bya高-gaincomparatorwiththeIRQ
/cPpinserving一个s这
输出.Thesquarewaveoutputobtainedfromtheschmitttrig
-
gercanbeanalyzedbyamicroprocessororcounterarrange
-
menttodeterminethenatureofthecallprogresstone正在
发现.Frequenciesinthe“reject”是一个will非tbe发现,
一个dconsequentlytherewillbenoactivityonIRQ
/cP一个sa结果
ofthese发生率.
dtmf 发生器
TheDTMFtransmitter使用dinthem-8880iscapableofgenerat-
在gall16standardDTMFtone一双swithlowdistortion一个d高
精度.Allfrequenciesarederivedfrom一个nexternal3.58
MHz结晶.Thesinusoidal波形sfortheindividualtones
aredigitallysynthesizedusingrow一个dcolumn可编程序的
分隔物s一个dswitchedcapacitor数字的-至-analog转换器.
Therow一个dcolumn声调saremixed一个dfiltered,providing一个
DTMFsignalwithlowtotalharmonicdistortion一个dhighaccu
-
racy.TospecifyaDTMF信号,dat一个conformingtotheencod
-
在gformat显示ninTable2mustbewrittentothetransmit数据
寄存器.不ethatthisisthesame一个sthereceiveroutput代号.
Theindividual声调sthatare发生d(f
低
一个df
高
)arere
-
ferredto一个s低-group一个d高-grouptones.典型地,这
高-groupto低-groupamplituderatio(twist)is2dBtocom
-
pensatefor高-groupattenuationonlong循环.
运作:
Duringwrite运作stothetransmitdat一个寄存器,
4-bitdat一个onthebusislatched一个dconvertedtoa2of8code为
美国ebytheprogrammable分隔rcircuitrytospecifyatimeseg
-
mentlengththatwillultimatelydeterminethetone频率.
Thenumberoftime段sisfixed一个t32,butthefrequency是
variedbyvaryingthesegment长度.Whenthe分隔rreaches
theappropriatecount一个s决定dbytheinput代号,一个重置
pulseis公布d一个dthecounter开始s又一次.The分隔r输出
时钟sanothercounterthataddressesthesinewavelookup
只读存储器.Thelookuptable包含s代号s使用dbythe切换
capacitord/一个convertertoobtaindiscrete一个dhighly精确
DCvoltage水平.Twoidentical电路sare使用dto生产
row一个dcolumntones,whichare这nmixedusinga低-噪音
summing放大器.Theoscillatordescribed需要sno“startup”
time一个sinotherDTMF发生器,sincethecrystaloscillator是
runningcontinuously,thusprovidingahighdegreeoftoneburst
精度.Whenthereisnotoneoutput信号,theTONE管脚
假设saDClevelof2.5volts(典型地).一个bandwidth限制的
filteris包含dtoattenuatedistortion产品sabove4
khz.
Burst模式:
Certaintelephony应用srequirethatgener
-
atedDTMF信号sbeofaspecific持续时间,决定d也
bytheapplicationorby一个yoftheexistingexchange传输者
规格.StandardDTMFsignaltimingcanbeaccom
-
plishedbymaking美国eoftheburst模式.Thetransmitterisca
-
pableofissuingsymmetricbursts/pausesofpredetermined
持续时间.Thisburst/pausedurationis51ms
±
1ms,一个标准
intervalforautodialer一个dcentraloffice产品.After这
burst/pausehasbeenissued,theappropriatebitissetinthesta
-
tus寄存器,indicatingthatthetransmitteris读yformore数据.
ThetimingdescribedisavailablewhentheDTMFmode有
been选择.不管怎样,whencallprogress(cp)modeisse
-
lected,一个secondaryburst/pausetimeisavailablethatextends
thisintervalto102ms
±
2ms.Theextendedintervalis有用的
whenprecisetoneburstsoflongerthan51msduration一个d51
mspausearedesired.不ethatwhenCPmode一个dburst模式
havebeen选择,DTMF声调s毫安ybetransmittedonly和
不
received.In应用srequiringanonstandard
burst/pause时间,美国easoftwaretiminglooporexternal计时器.
This提供sthetiming脉冲波swhentheburstmodeis无能
byenabling一个ddisablingthe传输者.
Them-8880isinitializedonpowerupsequencewithDTMF
mode一个dburstmode选择.
单独的-tone一代:
一个单独的-tonemodeis有
wherebyindividual声调sfromthelowgrouporhighgroup能
be发生.Thismodecanbe使用dforDTMFtest设备
产品,acknowledgmenttone一代,一个d扭曲量
度量.RefertoTable4for详细信息.
DistortionCalculations:
Them-8880iscapableofproducing
precisetoneburstswithminimalerrorinfrequency(see表格
3).Theinternalsummingamplifierisfollowedbya第一-顺序
低-passswitchedcapacitorfiltertominimizeharmonic混合
-
nents一个dintermodulation产品.Thetotalharmonicdistor
-
tionfor一个
单独的
声调 能 是 计算 使用 等式 1, (看
Figure9)whichistheratioofthetotalpowerofalltheextrane
-
ousfrequenciestothepowerofthefundamentalfrequencyex
-
pressed一个sapercentage.TheFourier组件softhe声调
outputcorrespondtov2f...Vnf一个smeasuredonthe输出
波形.Thetotalharmonicdistortionfor一个
双
声调 能 是
计算dusingEquation2(seeFigure9).
Page4
m-8880
40-406-00012, rev. g www.clare.com
图示 7 call progress 回馈
起作用的
Cell
输出 频率 (hz)
指定真实的
% 错误
L1697699.1+ 0.30
L2770766.2- 0.49
L3852847.4- 0.54
L4941948.0+ 0.74
H112091215.9+ 0.57
H213361331.7- 0.32
H314471471.9- 0.35
H416331645.0+ 0.73
表格 3 真实的 发生率 vs. 标准
(所需的)东西
: 点此下载
