in MT8870 DTMF decoder?

[mai fouad]

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!!!

 

[tpetar]

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.

http://hackedgadgets.com/wp-content/uploads/2010/01/mt8870_dtmf_decoder_datasheet.pdf

DTMF Decoder Board
http://www.razorconcepts.net/dtmf.html