in MT8870 DTMF decoder?

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mai fouad

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please i did not understand how the output std is working .and how to find the dial pulse duration so that i can take the output when only there is new output and not duplicate the output or skip one value of the output!!!
 

Did you check datasheet?

StD
Delayed Steering (Output). Presents a logic high when a received tone-pair has been registered and the output latch updated, returns to logic low when the voltage on St/GT falls below Vtst.

EsT
Early Steering (Output). Presents a logic high once the digital algorithm has detected a valid tone pair (signal condition). Any momentary loss of signal conditionwill cause ESt to return to a logic low.

St-Gt
Steering Input/Guard time (Output) Bidirectional. A voltage greater than Vtst detected at St causes the device to register the detected tone pair and update the output latch. A voltage less than V
TSt frees the device to accept a new tone pair. The GT output acts to reset the external steering time-constant, its state is a function of ESt and the voltage on St.

TOE
Three State Output Enable (Input). Logic high enables the outputs Q1-Q4. This pin is pulled up internally.

Q1-Q4
Three State Data (Output). When enabled by TOE, provide the code corresponding to the last valid tone-pair received (see Table 1). When TOE is logic low, the data outputs are high impedance.

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