Abstract: Has outlined MSM7512BRS many in the long-distance range machine main from the type correspondence application, introduced in detail this component’s pin function and the working, have given in the actual project application communications system’s principle of work which is composed of the computer and the monolithic integrated circuit, and carries on the analysis to its work process.
Key word: MSM7512BRS; AT89C52; RS-232; MAXl488
1 outline
Along with the computer technology and communication’s development, the data communication already became one application widespread mailing address, it uses the communications system the digit, the letter as well as the character carries on by the binary mode between the computer the transmission, the exchange and processing. The data communication may between 2 and 2 above microcomputers, the microcomputer and the monolithic integrated circuit as well as the monolithic integrated circuit and the monolithic integrated circuit carries on, through the correspondence channel (for example public telephone network, optical fiber channel, microwave channel, satellite channel) connects the machine. The monolithic integrated circuit main achievement from machine, widely uses in areas of technology and so on self-supervisory, survey, control. But the microcomputer as the main engine, installs in the condition superior environment. Between the monolithic integrated circuit and the microcomputer uses the public telephone network to realize the long range data correspondence through MO-DEM, its functional block diagram as shown in Figure 1.
2 MSM7512BRS synopses
MSM7512BRS is the FSK modem which Japanese OKI Corporation produces, this component conforms to the ITU-TV.23 rule, uses the half-duplex the working, the baudrate is 1200 kb/s; Has 75 kb/s baudrate reverse transmission path; Low power loss: Working pattern next 25 mW (VDD=5 V) and 9 mW (VDD=3 V); Conserves energy under the pattern for 100μw; Built-in mix resistive-capacitive circuit; Built-in analogous circuit link self-checking function; Built-in 3.58 MHz crystal oscillating circuit; The digital input/output interface and the TTL level is compatible.
MSM7512BRS uses 16 pin DIP seal, its pin function showed that like table l arranges in order.
MSM7512BRS chooses four workings by MODI and the MOD2 pin. Concrete working like table 2 arrange in order. Way 1 for simplex working way. When XD=l, the AO port’s sending signal frequency is l 300Hz, when XD=0, the AO port’s sending signal frequency is 2 100 Hz. Accepting circuit simulation input end AI and accepting circuit data out-port RD and internal electric circuit separation; Way 2 for full-duplex working. Receives 1 200 bit/s signal at the same time also by 75 bit/s speed transmission answering signals, when its signaling frequency XD=l is 390Hz, when XD=O is 450 Hz. The way 3 to simulate the circle self-checking working. From XD end input digital signal after chip in tone circuit, transmission bandpass filter and demodulation electric circuit, by RD end output digit signal, thus examination chip internal function to be whether correct; Way 4 for energy conservation working, this time chip biggest power loss for 100μW.
3 MSM7512BRS in correspondence application
Single power source MSM7512BRS may use in designing the high speed, the high performance communication network very conveniently. It has the periphery part number to be few, the working voltage scope is wide, driving force strong and so on characteristics, may widely apply in the remote control system, domains and so on long range communication system, through wired or wireless communication way clear signal transmission. In the wire transmission way, may use the special-purpose double thread network, may also carry on the transmission through the telephone line. It is composed with the telephone line interface circuit by 600Ω the impedance audio transformer exterior input/output voltage alignment circuit. On online transmits the signal voltage and the integrated circuit receive the signal voltage may establish independently according to the actual need.
3.1 main engines use computer’s data transmission way
MSM7512BRS and PC machine interface circuit as shown in Figure 2.
MAXl488E is uses under the adverse circumstance four group of low power loss line driver, its input and the TTL level are compatible. Around the electro-optic isolating circuit may shut off the electric circuit electricity direct relation, eliminates the grounding impedance and the long-distance range potential difference the influence which produces to the computer. When system transmission data, the computer sends out the data signal after MAXl488E the RS-232 level switch is the TTL level, then carries on after the electro-optic isolating circuit the signal connection in the MSM7512BRS XD end the modulation, modulates the FSK signal transmits again after the signal processing electric circuit after the telephone line. When receives the data, by telephone line input simulated signal after signal processing electric circuit, the output FSK signal enters MSM7512BRS the AI port to carry on the demodulation, isolates the MAXl488E component from the RD end output digit signal after the electro-optic, may be the RS-232 level input computer carries on the TTL level switch processing.
3.2 from machine use monolithic integrated circuit’s data transmission way
MSM7512BRS modem’s XD and the RD end electricity average and the TTL level are compatible, may with monolithic integrated circuit’s serial port direct connection, monolithic integrated circuit’s P1.O mouth and AOG is connected, chooses the analog output the enlargement factor; PI.1 and P1.2 with MODI, MOD2 are separately connected, use in choosing the working; P1.3 and TEXT are connected, with P1.1, P1.2 controls the chip together self-checking, P1.4 and RS is connected, controls the MSM7512BRS transmission or the received signal; P1.5 and CD connected determination receive signal and answering signal to be whether effective. Concrete electric circuit as shown in Figure 3.
The work process is as follows: The telephone line takes the simulated signal, after the C1 filter, the amplifier enlarges, finally transmits the modem MSM7512BRS AI end, then becomes the digital signal in the RD end to deliver monolithic integrated circuit AT89C52 the RXD end. Otherwise, the digital signal sends out by the monolithic integrated circuit AT89C52 TXD end, after the modem MSM7512BRS modulation, the simulated signal passes through two level of enlargement adjustments to transmit in again the telephone line. If selects the method which the special line transmits, then may connect directly with the transmission network, does not need the audio transformer.
4 concluding remark
The control circuit must with from machine carry on the electro-optic to isolate, uses in around the cut-off on the electric circuit electricity direct relation, eliminates the grounding impedance and the long-distance range potential difference to the monolithic integrated circuit the influence, meanwhile may avoid the electric shock causing the big area the batardeau to be bad. This plan use modem, realizes the long-distance range serial communication through the public telephone network, the signal distance may reach above 10 km, the baudrate reaches above 9600 b/s, hangs above radio station several 128, realizes between the computer and monolithic integrated circuit’s long-distance range data communication.
