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The development of the terminal of breath of fixed telephone short message that
From;    Author:Stand originally
(dispatch of network of world of Hua Jiang electron) The article gave out one kind gives priority to the design of the terminal of breath of fixed telephone short message that accuses CPU with 80C31, the design method that from systematic soft hardware two respects say to palpability secures terminal of breath of telephone short message and the working principle of each parts. To the difficulty that encounters in development, if CAS sound detects, the processing of FSK information and character of LCD Chinese character show waited for issue focal point to undertake elaborating.

Keyword: The short message ceases; Phone; DTMF; FSK

Now, short news service gains ground increasingly. Each phone manufacturer are designed eagerly and develop telephone of short information terminal. The short information terminal that develops to cooperate me is special and compositive chip, our design developed the fixed telephone call that can be sent and accepts short message interest. This phone is divided outside having an incoming telegram to display a function, still can receive the FSK format short message that sends below information center, can use DTMF and FSK two kinds of formats upload information. Have better man-machine interface, can use phoneticize to input a method to edit short message content. Can store 200 phones, the short message of 200 download, implement telephone number search, download a short message read, clock shows wait for a function. Systematic design introduces from hardware respect first below.

   Hardware part

Pursue block diagram of principle of 1 system hardware

Pursue 2 CAS detects principle circuit

Block diagram of systematic hardware principle sees a picture 1, the function of departmental cent explains below.

   CPU controls a share

80C31 is used to regard as in the system advocate accuse CPU, be in charge of the order flow of whole system, outside enlarge 32K RAM, 64K EPROM, regard a phone as the memory of thin, short information and matrix of 2 class font with the AT29C040A of an ATMEL company.

   CAS detects circuit

CAS detects principle circuit is shown 2 times like the graph. In short message phone, of CAS signal detecting is indispensable, but indication phone of the average telephone call previously and incoming telegram does not have this function, CAS sound is had to detect on the market functional chip is scarcer also, accordingly, we designed sound of a kind of CAS to detect circuit, in applying actually, the result is right (3) seeing a picture.

CAS is DTMF signal, frequency is 2130/2750Hz, use two alone filter so, if be CAS, criterion A, b nods output to all be tall n, generation CAS is interrupted. The SIGNAL in the graph is DTMF signal, CAS_CON detects for CAS sound control circuit, when CAS_CON=1, detect CAS sound; When CAS_CON=0, do not detect CAS sound. Should detect CAS, CASINT outputs tall n.
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