Agilent 5989-6580EN RS-232 Troubleshooting - Application Note c20140910 [8] free download

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Keysight Technologies RS-232 Troubleshooting Application Note Introduction In the course of dealing with personal computers, you may use the RS-232 serial interface. This application note will describe RS-232 at a basic level, with an orientation towards Windows-based instrument programming. 1. An Overview of RS-232 The irst question that needs to be addressed is: what precisely is a "serial" interface? Consider a computer connected to an instrument or other "remote" device. One of the simplest possible communications schemes is shown in Figure 1. Each device sends data bits coded as electrical pulses, with a "0" corresponding to a low voltage and a "1" a high voltage, to the other over a dedicated line, using a shared ground line. Using separate lines to transmit and receive data allows both devices to send data simultaneously without interference, at least in principle. For example, to send a byte to the remote device, the computer would have to send as shown in Figure 2. There are a wide variety of serial communications schemes. The most popular is RS-232, which is in fact so universal that it is often simply referred to as "serial." RS-232 deines various mechanical and electrical specs for serial communications. Output Input RS-232 deines legal voltage levels as follows: 0 (mark) +5 to +3 to +15 volts DC +15 volts DC 1 (space)