欢迎访问ic37.com |
会员登录 免费注册
发布采购

MT8880CS-1 参数 Datasheet PDF下载

MT8880CS-1图片预览
型号: MT8880CS-1
PDF下载: 下载PDF文件 查看货源
内容描述: ISO2 -CMOS集成DTMFTransceiver [ISO2-CMOS Integrated DTMFTransceiver]
分类和应用:
文件页数/大小: 18 页 / 315 K
品牌: MITEL [ MITEL NETWORKS CORPORATION ]
 浏览型号MT8880CS-1的Datasheet PDF文件第1页浏览型号MT8880CS-1的Datasheet PDF文件第2页浏览型号MT8880CS-1的Datasheet PDF文件第3页浏览型号MT8880CS-1的Datasheet PDF文件第5页浏览型号MT8880CS-1的Datasheet PDF文件第6页浏览型号MT8880CS-1的Datasheet PDF文件第7页浏览型号MT8880CS-1的Datasheet PDF文件第8页浏览型号MT8880CS-1的Datasheet PDF文件第9页  
MT8880C/MT8880C-1 ISO2-CMOS  
Steering Circuit  
Guard Time Adjustment  
Before registration of a decoded tone pair, the  
receiver checks for a valid signal duration (referred  
to as character recognition condition). This check is  
performed by an external RC time constant driven by  
The simple steering circuit shown in Figure 5 is  
adequate for most applications. Component values  
are chosen according to the formula:  
ESt. A logic high on ESt causes v (see Figure 5) to  
rise as the capacitor discharges. Provided that the  
signal condition is maintained (ESt remains high) for  
c
t
= t +t  
DP GTP  
REC  
t =t +t  
ID DA GTA  
the validation period (t  
), v reaches the threshold  
GTP  
c
The value of t  
Electrical Characteristics) and t  
is a device parameter (see AC  
(V ) of the steering logic to register the tone pair,  
DP  
TSt  
is the minimum  
latching its corresponding 4-bit code (see Figure 7)  
into the Receive Data Register. At this point the GT  
output is activated and drives v to V . GT  
continues to drive high as long as ESt remains high.  
Finally, after a short delay to allow the output latch to  
settle, the delayed steering output flag goes high,  
signalling that a received tone pair has been  
registered. The status of the delayed steering flag  
can be monitored by checking the appropriate bit in  
the status register. If Interrupt mode has been  
REC  
signal duration to be recognized by the receiver. A  
value for C1 of 0.1 µF is recommended for most  
applications, leaving R1 to be selected by the  
designer. Different steering arrangements may be  
used to select independently the guard times for tone  
c
DD  
present (t  
) and tone absent (t  
). This may be  
GTP  
GTA  
necessary to meet system specifications which place  
both accept and reject limits on both tone duration  
and interdigital pause. Guard time adjustment also  
allows the designer to tailor system parameters such  
as talk off and noise immunity.  
selected, the IRQ/CP pin will pull low when  
delayed steering flag is active.  
the  
The contents of the output latch are updated on an  
active delayed steering transition. This data is  
presented to the four bit bidirectional data bus when  
the Receive Data Register is read. The steering  
circuit works in reverse to validate the interdigit  
pause between signals. Thus, as well as rejecting  
signals too short to be considered valid, the receiver  
will tolerate signal interruptions (drop out) too short  
to be considered a valid pause. This facility, together  
with the capability of selecting the steering time  
constants externally, allows the designer to tailor  
performance to meet a wide variety of system  
requirements.  
tGTP = (RPC1) In [VDD / (VDD-VTSt)]  
tGTA = (R1C1) In (VDD/VTSt  
)
R
P = (R1R2) / (R1 + R2)  
VDD  
C1  
R2  
St/GT  
R1  
ESt  
a) decreasing tGTP; (tGTP < tGTA)  
VDD  
tGTP = (R1C1) In [VDD / (VDD-VTSt  
tGTA = (RpC1) In (VDD/VTSt  
RP = (R1R2) / (R1 + R2)  
)
)
C1  
VDD  
VDD  
Vc  
St/GT  
ESt  
C1  
R1  
St/GT  
tGTA = (R1C1) In (VDD / VTSt  
)
R1  
R2  
tGTP = (R1C1) In [VDD / (VDD-VTSt)]  
ESt  
MT8880C/C-1  
b) decreasing tGTA; (tGTP > tGTA)  
Figure 5 - Basic Steering Circuit  
Figure 6 - Guard Time Adjustment  
4-36