中英文翻译--RS-232通信协议及接口标准【适用于毕业论文外文翻译】.doc

英文文献 RS-232 communications agreements and standard interfaces RS-232C outlined Serial communications interface standards through the use and development, there are already several. But in RS-232 standards are improved, and formed the basis. RS-232C U.S. EIA (Electronic Industry Association), together with the Bell companies in 1969 announced the development of communication agreement. It 020000b/s suitable for data transmission rate in the context of communications. This standard for serial communications interface on the issues, such as signal line functions, electrical characteristics were clearly defined. Since passage of the production equipment manufacturers are compatible with RS-232C standard communications equipment, and therefore it as a standard, is now widely used in computer communications interface. In discussing the content of RS-232C interface standards before on two points : First, long-range communications link initially RS-232C standard data terminal equipment DTE (Data Terminal Equipment) and data communications equipment DCE (Data Communication Equipment) developed. Therefore the standards and does not consider the application of computer systems. But now it was widely borrowed for computers (more accurately, is a computer interface) between the scales of engineered with terminal or connecting standard. Clearly, some of the requirements and standards and computer systems is inconsistent, and even contradictory. With this background knowledge, we RS-232C computer incompatible with the standards of local not difficult to understand. Secondly, RS-232C criteria mentioned sending and receiving are standing DTE position, rather than standing at the position of DCE to the definition. In computer systems, often between the CPU and I/O Equipment transmission of information both DTE and therefore both sending and receiving. RS-232C interface standards RS-232C standards (agreement) is the full names EIA-RS-232 standards, including EIA (Electronic Industry Association), speaking on behalf of the U.S. Electronics Industry Association, Rs ( Recommeded standard), speaking on behalf of recommended standards, 232 is the identification number, the latest revision C representative RS232 (1969), in the meantime, RS232B, RS232A. . It provides connecting cables and mechanical, electrical characteristics, functions and signal transmission process. There are also common physical standard EIARS-232-C, EIARS-422-A, EIARS-423A, EIARS-485. Here only on EIARS-232-C (short for 232,RS232). For example, the IBM PC machines currently in the COM1, COM2 interface is RS-232C interfaces. (1) electrical characteristics EIA-RS-232C for electrical characteristics, functional logic of peaceful various signal lines are provided. In the TXD and RXD : Logic 1 (Mark) =-3V-15V, logic 0 (space) =+3+15V In the RTS, CTS, DSR,DTR, and DCD control line : Signal effective (connected, on state is voltage) =+3V+15V, signal void (break apart, the off state, a negative voltage) =-3V-15V The above provisions on the criteria of logic call RS-323C Ping definition. The data (information code) : logic 1 (-) electricity ping below -3V, logic 0 (air) than the call ping +3V; for control signals; connected state (5B6) that the effective signal than +3V call ping, break apart state (off) that signals invalid call ping below -3V, When Ping is the absolute power transmission than 3V, the circuit can effectively check out somewhere between the voltage meaningless -3+3V below or above +15V -15V the voltage believe meaningless, and therefore, the actual work should be guaranteed in the electric ping + (315) V between. (2) the mechanical properties connectors As RS-232C not defined connectors physical characteristics, and therefore there DB-25, DB-15 and DB-9 various types of connectors, Leads feet definitions vary. The two connectors were introduced. （1） DB-25 connectors PC and XT machines used DB-25 type connectors. DB-25 connectors definition of a root signal line 25, divided into four groups : asynchronous communications nine voltage signals (including signal to SG) 2,3,4,5,6,7,8,20,22 Central 20mA current signal 9 (12,13,14,15,16,17,19,23,24) Air 6 (9,10,11,18,21,25) Protectorate (PE) 1 as equipment grounded ends (one foot) Attention 20mA current signal only part PC/XT IBM PC and IBM machines to provide to at plane and beyond, is not supported. （2） DB-9 connectors In at plane and beyond, do not support 20mA current link interfaces, the use of DB-9 connectors, as a card or main board, with multifunctional I/O COM1 and COM2 two serial interface Link the connectors. It provides asynchronous communications nine signals. DB-25 type connectors Leads feet distribution and the type Leads feet DB-25 signal completely different. Therefore, if the allocation to the DCE DB-25 type connectors connecting equipment to use specialized cables lines. Cable length : In communications rate below 20kb/s, RS-232C direct physical distance of 15m from the largest (50 feet). Largest direct transmission distance Note : RS-232C standards require that if the use of modem, code distortions in less than 4% of the maximum transmission distance between DTE and DCE for 15m (50 ft). It is the largest distance in yards per distortions less than 4% given the premise. To ensure that codes for less than 4% of the distortions, interface standards in the electrical properties that, the drive should be less than 2500pF load capacitance. (3) the interface signals RS-232C Figure 2-2 RS-232 leads feet Figure RS-232C conventional standards interface 25 lines, four lines of data, 11 Line of Control, 3 regular lines, 7 standby and missing lines, commonly used only nine roots, and they are : Liaison control signal lines : Data ready devices (Data set ready-DSR) - effective (on) state that could be used modem in the state. Data terminal ready (Data Terminal ready-DTR) - effective (on) state that data terminals can be used. Sometimes even to the power of these two signals, one on the call immediately effective. Two state signals effective equipment, but indicated that the equipment itself could be used, does not indicate a communication link can initiate communication can begin by following communication to the control signals. Request sent (Request to send-RTS) - used to express DTE DCE request sent data to be sent when data terminals, so that a signal (on state), a request sent to modem. It is used to control access to state modem. Allow transmission (Clear to send-CTS) - used to express DCE DTE made ready to receive the data signal is sent to request the response RTS signal. When modem is ready to receive data transmitted from terminal, and move to, so that the effective signal to inform terminals begin sending data along the lines TXD sending data. This request received RTS/CTS contact signal is sent to 3,600-4,000 modem system between the cut over ways and means to receive. In Full two-way work system for transmission and reception of way between the cut over. In Full two-way work system for the allocation of two-way routes, so there is no need RTS/CTS contact signals to change high. Receive line signals departure clearance (Beijing Line detection-RLSD) - used to express DCE has connected communications links to inform DTE ready to receive data. When local modem received by the other side of communication links (distant) modem sent to the carrier signal, the signal RLSD effective, informed terminal ready to receive, and will receive from modem demodulate signals from the carrier into the digital traffic data, along RXD line toreceive data terminals. The line is also known as data carrier departure clearance (Data carrier detection-DCD) line. Ringing instructions (Ringing-RI) - When modem sent the switchboard received Ringing call sign, signal to the effective (on state), informed terminals have been shouting. Send and receive data lines : Send data (Transmitted data-TXD) - through TXD serial data terminals will be sent to modem, (DTEDCE)。 Receiving data (Beijing data-RXD) - through RXD line terminals receive data from modem made to the serial，(DCEDTE)。 Earth There are two lines SG, PG- signal to the signal line and the protection, without direction. The control signal line when effective, and when the order expressed interface signal transmission process. For example, only when DSR and DTR are in the effective (on) status, can be transmitted between the DTE and DCE operation. If the DTE to send data, the advance will buy into effective DTR line (on) status, such as CTS line received effective (on) of the answer, can send serial data at TXD line. This sequence of the provisions of Half of the two-way work lines of communication particularly useful because duplex communication can be determined by the DCE to receive directions to the direction of this line can begin sending. RS-232通信协议及接口标准 RS-232C概述 串行通信接口标准经过使用和发展，目前已经有几种。但都是在RS-232标准的基础上经过改进而形成的。RS-232C是美国EIA(电子工业联合会)与BELL等公司一起开发的1969年公布的通信协议。它适合于数据传输速率在020000b/s范围内的通信。这个标准对串行通信接口的有关问题，如信号线功能、电器特性都作了明确规定。由于通行设备厂商都生产与RS-232C制式兼容的通信设备，因此，它作为一种标准，目前已在微机通信接口中广泛采用。 在讨论RS-232C接口标准的内容之前，先说明两点： 首先，RS-232C标准最初是远程通信连接数据终端设备DTE(Data Terminal Equipment)与数据通信设备DCE（Data Communication Equipment）而制定的。因此这个标准的制定，并未考虑计算机系统的应用要求。但目前它又广泛地被借来用于计算机（更准确的说，是计算机接口）与终端或外设之间的近端连接标准。显然，这个标准的有些规定及和计算机系统是不一致的，甚至是相矛盾的。有了对这种背景的了解，我们对RS-232C标准与计算机不兼容的地方就不难理解了。 其次，RS-232C标准中所提到的“发送”和“接收”，都是站在DTE立场上，而不是站在DCE的立场来定义的。由于在计算机系统中，往往是CPU和I/O设备之间传送信息，两者都是DTE，因此双方都能发送和接收。 RS-232C接口标准 RS-232C标准(协议)的全称是EIA-RS-232标准, 其中EIA(Electronic Industry Association)代表美国电子工业协会，RS（Recommeded standard）代表推荐标准，232是标识号，C代表RS232的最新一次修改（1969），在这之前，有RS232B、RS232A。它规定连接电缆和机械、电气特性、信号功能及传送过程。常用物理标准还有有EIARS-232-C、EIARS-422-A、EIARS-423A、EIARS-485。 这里只介绍EIARS-232-C（简称232，RS232）。 例如，目前在IBM PC机上的COM1、COM2接口，就是RS-232C接口。 (1) 电气特性 EIA-RS-232C对电器特性、逻辑电平和各种信号线功能都作了规定。 在TXD和RXD上： 逻辑1(MARK)=-3V-15V，逻辑0(SPACE)=+315V 在RTS、CTS、DSR、DTR和DCD等控制线上： 信号有效（接通，ON状态，正电压）+3V+15V，信号无效（断开，OFF状态，负电压）=-3V-15V 以上规定说明了RS-323C标准对逻辑电平的定义。对于数据（信息码）：逻辑“1”（传号）的电平低于-3V，逻辑“0”（空号）的电平高于+3V；对于控制信号；接通状态（ON）即信号有效的电平高于+3V，断开状态(OFF)即信号无效的电平低于-3V，也就是当传输电平的绝对值大于3V时，电路可以有效地检查出来，介于-3+3V之间的电压无意义，低于-15V或高于+15V的电压也认为无意义，因此，实际工作时，应保证电平在(315)V之间。 （2） 连接器的机械特性 由于RS-232C并未定义连接器的物理特性，因此，出现了DB-25、DB-15和DB-9各种类型的连接器，其引脚的定义也各不相同。下面分别介绍两种连接器。 1）DB-25连接器 PC和XT机采用DB-25型连接器。DB-25连接器定义了25根信号线，分为4组： 异步通信的9个电压信号（含信号地SG）2，3，4，5，6，7，8，20，22 20mA电流环信号 9个（12，13，14，15，16，17，19,23，24） 空6个（9，10，11，18，21，25） 保护地（PE）1个，作为设备接地端（1脚） 注意，20mA电流环信号仅IBM PC和IBM PC/XT机提供，至AT机及以后，已不支持。 2）DB-9连接器 在AT机及以后，不支持20mA电流环接口，使用DB-9连接器，作为提供多功能I/O卡或主板上COM1和COM2两个串行接口的连接器。它只提供异步通信的9个信号。DB-25型连接器的引脚分配与DB-25型引脚信号完全不同。因此，若与配接DB-25型连接器的DCE设备连接，必须使用专门的电缆线。 电缆长度：在通信速率低于20kb/s时，RS-232C所直接连接的最大物理距离为15m（50英尺）。最大直接传输距离说明：RS-232C标准规定，若不使用MODEM，在码元畸变小于4%的情况下，DTE和DCE之间最大传输距离为15m（50英尺）。可见这个最大的距离是在码元畸变小于4%的前提下给出的。为了保证码元畸变小于4%的要求，接口标准在电气特性中规定，驱动器的负载电容应小于2500pF。（3） RS-232C的接口信号图2-2 RS-23