【正文】 ristic did had stipulated explicitly. Because the general equipment manufacturer produces with the RS232C service pattern patible munication facility, therefore, it takes one kind of standard, at present already in microputer correspondence connection widespread use. Before discussing the RS232C interface standard the content, explains two points first: First, the RS232C standard is at first longdistance correspondence connection data terminal equipment DTE (Data Terminal Equipment) (Data Communication Equipment) formulates with data transmission set DCE. Therefore this standard formulation, has not considered puter system39。 RS232C, EIAamp。 RS423A, EIAamp。 RS232C (. 232, RS232). For example, in IBM PC machine on COM1, the COM2 connection, is the RS232C connection at present. 1. electrical specification EIARS232C to the electric appliance characteristic, the logic level and each kind of holding wire function has made the stipulation. on TxD and RxD: Logical 1(MARK)=3V~15V logical 0(SPACE)=+3~+15V on pilot wires and so on RTS, CTS, DSR, DTR and DCD: signal effective (connection, ON condition, positive voltage) =+3V~+15V signal invalid (separation, OFF condition, negative voltage) =3V~15V The above stipulation showed the RS323C standard to the logic level definition. Regarding data (information code): Logic “1” (mark) the level is lower than 3V, logic “0” (blank) the level considers language +3V。 (3~15)V. EIARS232C and TTL transformation: EIARS232C is expresses the logical condition with the positive and negative voltage, with TTL by height level expression logic The condition stipulation is different. Therefore, for can with the puter connection or the terminal TTL ponent connection, must carries on the level and the logical relation transformation in EIARS232C and between the TTL electric circuit. Realizes this kind of transformation method available discrete ponent, also available integrated circuit chip. At present widely uses the integrated circuit to transform the ponent, like MC1488, the SN75150 chip may plete the TTL level to the EIA level transformation, but MC1489, SN75154 may realize the EIA level to the TTL level transformation. The MAX232 chip might plete TTL←→EIA the bidirectional level switch, Figure 1 has demonstrated 1488 and 1489 internal structures and the pin. The MC1488 pin (2), (4,5), (9,10) and (12,13) meet the TTL input. Pin 3, 6, 8, 11 output termination EIARS232C. MC1498 14 1, 4, 10, 13 feet meet the EIA input, but 3, 6, 8, 11 feet meet the TTL output. Concrete connection method as shown in Figure 2. In the chart left side is in microputer serial interface electric circuit39。s definition is also various. Below introduces two kind of couplings separately. (1) DB25: PC and XT machine uses the DB25 coupling. The DB25 coupling has defined 25 holding wires, divides into 4 groups: ①Asynchronous munication 9 voltage signal (including signal SG) 2,3,4,5,6,7,8,20,22 ②20mA electric current link signal 9 (12,13,14,15,16,17,19,23,24) ③Spatial 6 (9,10,11,18,21,25) ④The protectorate (PE) 1, takes the equipment ground terminal (1 foot) The DB25 coupling39。//使能端E為P1^2口sbit lcdrw=P2^1。 void delay(uint z)。//LCD初始化子函數(shù)聲明void main(){ uint i。//顯示第1行 delay(3)。 delay(3)。i14。i24。//停3秒 write_(0x08)。 write_(0x08)。 write_(0x08)。 delay(3000)。 for(i=0。 } write_(0x80+0x53)。i++) { write_date(table1[i])。 for(i=0。i++) { write_date(table[i])。 write_(0x80+0x10)。 write_(0x0c)。 write_(0x0c)。 write_(0x0c)。//1c delay(300)。 delay(3)。//顯示第2行 delay(3)。i16。 delay(600)。//寫指令子函數(shù)聲明void write_date(uchar date)。//數(shù)據(jù)/指令選擇端RS為P1^0口uchar const table[]=Good Good Study 。s maximum physical distance is 15m (50 feet). The maximum direct transmission distance explained: RS232C standing operating procedure, if does not use MODEM, in the element distortion is smaller than in 4% situations, between DTE and DCE the maximum transmitting range is 15m (50 feet). Obviously this maximum distance is in the element distortion is smaller than under 4% premises gives. In order to guarantee that the element distortion is smaller than 4% requests, the interface standard stipulated in the electrical specification, driver39。s physical characteristics: Coupling: Because RS232C has not defined coupling39。 The connection condition (ON) is the signal effective level is higher than +3V, disconnect state (OFF) is the signal invalid level is lower than 3V, is also when transmission level39。 RS485. Here only introduces EIAamp。 RS422A, EIAamp。s understanding, we were not difficult to the RS232C standard and the puter inpatible place to understand. Next, in the RS232C standard mentioned “the transmission” and “the receive”, stands in the DTE standpoint, but not stands in the DCE standpoint defines. Because in the puter system, often is CPU and between the I/O equipment the passalong message, both are DTE, therefore both sides can transmit and the receive. one, RS232C RS232C standard (agreement) the full title is the EIARS232C standard, EIA (Electronic Industry Association) represents the US Electronic industry association, RS (emeded standard) represents the remended limit, 232 are marks the number, C represents RS232 the newest revision (1969), before then, has RS232B, RS232A. . It stipulates the tie cable and the machinery, the electrical specification, the signal function and the transmission process. The monly used physical standard also has EIAamp。為了保證碼元畸變小于4%的要求，接口標準在電氣特性中規(guī)定，驅動器的負載電容應小于2500pF。注意，20mA電流環(huán)信號僅IBM PC和IBM PC/XT機提供，至AT機及以后，已不支持。 連接器的機械特性： 連接器： 由于RS232C并未定義連接器的物理特性，因此，出現(xiàn)了DB2DB15和DB9各種類型的連接器，其引腳的定義也各不相同。MC1498的14的13腳接EIA輸入，而11腳接TTL輸出。目前較為廣泛地使用集成電路轉換器件，如MC148SN75150芯片可完成TTL電平到EIA電平的轉換，而MC148SN75154可實現(xiàn)EIA電平到TTL電平的轉換。(3～15)V之間。 例如，目前在IBM PC機上的COMCOM2接口，就是RS232C接口。RS485。RS422A、EIAamp。常用物理標準還有有EIAamp。 其次，RS232C標準中所提到的“發(fā)送”和“接收”，都是站在DTE立場上，而不是站在DCE的立場來定義的。因此這個標準的制定，并未考慮