Along with the technical swift development and living standards’ unceasing enhancement, handset’s popular rate is getting higher and higher, the renewal is also getting quicker and quicker, the price is also getting more and more cheap. Is broad because of the handset work’s wireless network coverage area, in information transmission aspect stable property, reliable, therefore takes the handset the information transmission the carrier, unifies the constitution application system with the monolithic integrated circuit to have the formidable vitality and the broad application space, specially in domains and so on long range data transmission, long-distance monitoring is receives the electronic design to apply engineer’s attention. Some specialized publications also introduced some concern this aspect article, however, because handset’s control command is complex, the data format is tedious, the engineers and technicians when carry on the monolithic integrated circuit and handset’s hard software interface design will encounter many difficulties frequently, sometimes has not had the material to be possible to look up. The author in completes a project in the performance history, has carried on the massive tests and the experiment in view of several kind of handsets, based on this induces some belt regular conclusion, regarding the conclusion, the engineering design personnel may bring namely use, reduces the research and development cycle greatly, now announces it, is willing to share with the general electron designers.
1 hardware interface technology aspect
At present in the market the popular majority of handsets nearly have the data to direct the export, basically and supports with GsM the short information related AT control command (GSM-SMS-AT instruction), handset through data mouth by serial mode receive instruction and outward output data. Theoretically says, discovered RxD, TxD and the GND pin and monolithic integrated circuit’s serial port correspondence connection in the data mouth namely has completed the hardware interface. However, because in fact the different brand, different model handset’s RxD, TxD and the GND pin is by no means consistent, looks looks up these three lines sometimes also the non-easy matter; Moreover the handset data mouth’s level is already not the RS232 level, is also not the TTL level, with the monolithic integrated circuit serial port which supplies power by 5V has not been able the direct connection. The simple reliable method is uses handset’s data line to establish the monolithic integrated circuit and handset’s hardware connection. The handset data line is to connect the PC machine 9 needle serial ports to design specially, signal level for standard RS232 level, so long as monolithic integrated circuit’s serial port also transformation is the Rs 2 3 2 levels, may facilitate the connection. 9 needle serial port pin definition is fixed, namely 2 feet are TxD (handset transmission), 3 feet are RxD (handset receive), 5 feet are GND. Thus, regardless of any model’s handset and monolithic integrated circuit’s connection has become the permanent connection, does not need to know that the handset data verbal message number the concrete definition, the two through data line junction circuit as shown in Figure 1.
What needs to pay attention: The different handset data line interior level switch chip’s power supply way is different, some are supplies power directly through the handset; Some are through steals PC machine serial port certain pins (usually are 4, 6, 7, 8 pins) the electric current after the internal rectification filter constant voltage provides. The judgment method is inserts a data line end to the handset data mouth, surveys another end 2 foot’s with 5 feet between voltages, if has about a 7V voltage, for the former, if could not measure that the voltage, for the latter, needs the monolithic integrated circuit regarding the latter is a 4, 6, 7, 8 pin pin provides the 5V voltage willfully then, like Figure 1 dashed line shows.
2 software interface technology and control principle
The monolithic integrated circuit and handset’s software interface is actually the monolithic integrated circuit through with GSM the short information related AT command control handset’s control technology, like reads handset’s short news content, deletes the short news content, lists short news which in the handset has not read and so on. Sees reference [1,2] about at instruction’s functional description the article content, here no longer gives unnecessary detail. However, carries out an instruction, also in certain material introduces that by no means simply. In fact, the instruction implementation needs the monolithic integrated circuit and the handset replies alternately completes, each transmission or the receive byte count has the strict stipulation, the two must rest on these stipulations to realize the data exchange, otherwise, the correspondence is the defeat. The author passes through to several kind of handsets tests repeatedly, summarizes some rules, like Table 1 arranges in order.
Is as follows to several question explanations.
①All AT instruction’s instruction mark, the constant, the PDu data packet and so on are transmit by the ASCII coded form, for instance “A” the ASCII code is 41H, “T” the AscII code is 54H, the digit “0, AsCⅡThe code is 30H and so on.
②The monolithic integrated circuit control handset work, must handset’s short information working pattern establishment be the PDu form, namely completes through instruction AT cMGF=O.
③Monolithic integrated circuit transmits each instruction after the handset, must take the carriage return symbol take this instruction the conclusion, the carriage return ASCII code as 0DH. For example, the monolithic integrated circuit to the handset transmission “AT CMGF=0″ this instruction, its ASCII coded sequence is “41H, 54H, 2BH, 42H, 4DH, 47H, 46H, 3DH, 30H, 0DH”, last byte 0DH is the carriage return symbol, indicated that this instruction ended, if did not have this carriage return symbol, the handset will not distinguish this instruction.
④When the handset receives after a complete AT instruction, the handset carries out this instruction not immediately, but first a moment ago received AT the instruction complete ASCII coded sequence instead transmits completely (including 0DH), then transmits a carriage return symbol and line feeds the symbol ASCII code, namely 0DH and 0AH, carry out this instruction finally.
⑤Handset when transmits the short information content to the monolithic integrated circuit, its PDu data packet’s content is by the hexadecimal system expression data, but is not directly to the monolithic integrated circuit transmission hexadecimal system data, but was still transmits each sexadecimal number by the AscII code. Thus, two byte’s sexadecimal numbers turn 4 byte ASCII codes. But, in the PDU data packet’s data byte length part was still the actual byte length, but is not turns the AscII code the byte length, this when programming should the special attention, otherwise, the receive data is incomplete. After the monolithic integrated circuit receives the PDU data packet data, must restore it the hexadecimal system data, its algorithm is as follows: Supposes a is the receive ASCII code, after b is the transformation sexadecimal number. If a<39H, then b=a-30H; If a>39H, then b=a-30H-07H, the around two number merges is a byte finally.
⑥The handset replies the PDU data packet byte count to the monolithic integrated circuit not including the first 9 byte data (short message service center address), but transmits time the PDU data packet to the monolithic integrated circuit, including these 9 byte data. For example, if the handset reply’s PDU data length is 50, but actual transmits to the monolithic integrated circuit the hexadecimal system data is 59 bytes, the ASCII code for 2×59 the byte, therefore, the monolithic integrated circuit must receive the PDU data according to 2×59 the byte.
3 application examples
The author used the above principle and a connection technology development project: Highway demonstration guiding system. Installs on front highway’s LED display monitor real time display the road section vehicles general situation and the weather weather condition, reminds and guides the driving personnel, correct driving. In this system’s use certain extent eliminated many traffic accident hidden danger, thus has safeguarded the path unimpeded and the people life and property security. This system is composed of the control center and certain display monitors. Control center real-time most recent message routing to various display monitors. The construction control center and alphanumeric display terminal’s information link, the traditional method either lays down the fiber optics to realize with the wired way, either constructs the special-purpose wireless net to realize with the wireless way. Because of highway’s particularity, between the control center and alphanumeric display terminal’s distance is very usually far, two kind of plans both must invest the massive funds and the huge construction work load. If uses the GSM public wireless transmission network, the control center transmits by the short information’s form the displayed information to the alphanumeric display terminal technical program, then has the investment to be small, the construction is convenient, operation reliable, operating cost low status many merits.
In control center, after microcomputer editor good short information, transmits through handset this carrier. In the alphanumeric display terminal, the monolithic integrated circuit through reads handset’s short information to demonstrate it on the LED display monitor. The project core technologies is the monolithic integrated circuit and handset’s connection and in the PDU data packet Chinese character information encoding. Because in the short information’s Chinese character is a code merely, the monolithic integrated circuit application system will code becomes the Chinese character lattice data, must dispose the Chinese character fonts. Stipulated according to the GSM07.05 agreement that in the short information’s Chinese character code is the Unicode code, if constructs a Unicode code the Chinese character fonts, is a tedious work truly, therefore, in design monolithic integrated circuit application system time, uses the following two technical measure.
①The monolithic integrated circuit system disposition’s fonts are the GB-2312 code Chinese character storehouse, namely the zone bit code Chinese character storehouse, this Chinese character storehouse on-line may the free download, solidifies to the Flash memory chip in then. Certainly does the premise is in the PDU data packet Chinese character code must for the Chinese character encoding, but non-Unicode code.
②When the control center edits the PDU data packet data, uses from the definition data mode, represents the Chinese character the data, uses the Chinese character directly machine the encoding then, has exempted machine the encoding transformation is pain of again the Unicode code. The practice proved that this is feasible.
Uses the above technical measure the merit; first, has omitted two kind of code interconversions; Second, had guaranteed the data secrecy, in the non-system the user is unable to receive, even if receives is also unable to demonstrate.
After this project develops is operational successfully, because the alphanumeric display terminal receive does not only transmit, does not have the run cost nearly. The transmitting end (control center) may select the monthly rent method, can also reduce the operating cost the threshold. Therefore this project obtains the user satisfactory appraisal.
