In RS232 Serial Communications, the abbreviation of RS stands for recommended slandered and the number 232 states the modern version. The serial communication systems were classified into different types, and that are used to transfer the data over large distances through some range of information cable. In telecommunications, the RS232 port formally describes the signals connecting between the DTE (data terminal equipment) and DCE (data circuit terminating equipment).The DTE is computer terminal and DCE is modems, or controllers etc.
Nowadays, most of the PCs have two serial ports and one parallel port namely, RS232. These ports are used to communicate with external devices. The parallel port (RS232) communicates at a time (sends and receives) with the 8-bit data over eight separate wires to transfer the data very fast. These parallel ports are normally used to connect a printer to a personal computer. This article gives the fundamentals of RS232 communication.
What is RS232 Serial Communication?
The RS-232 is a communication cable, used to send and receive the serial information between two devices. It supports the transmissions like synchronous and asynchronous. RS-232 communication cable is used in several devices of industrial environment. RS232 Serial Communication is used to recognize the difference of two signal levels (logic 1 and logic 0). Logic 0 and logic 1 are represented with +12V and -12V. The RS232 cable works at various baud rates such as 9600 bits/sec, 2400bits/sec, 4800bits/sec etc.
RS232 Pin Configuration
The pin configuration of RS232 Serial Communication is available in 9-pin RS232 and 25-pin RS232, each pin has its own function is as follows.However, most devices never need to use all of the pins, so the cabling requirements for specific devices may vary. Many common serial devices (modems for example), use a 9 pin serial connection.
RS-232 DB25 Pin Out
RS-232 DB9 Pin Out
How to Choose RS232 Cable?
The main consideration in selscting an RS232 Serial Communication cable includes the following
- What devices are to be connected? First, are you connecting two DTE devices or a DTE device to a DCE device?
- What connectors are necessary on every end, male (or) female, 25-pin or 9-pin?
- Usually, it is suggested that the user find the two devices to be connected, and then decide which cable is mandatory.
Specifications of RS232 Serial Communication
The voltage levele of transmitted signal are
- Binary 0: +5 to +15 Vdc
- Binary 1: -5 to -15 Vdc
The voltage level of received signal are
- Binary 0: +3 to +13 Vdc
- Binary 1: -3 to -13 Vdc
- Start bit: Binary 0
- Data: 5, 6, 7 or 8 bits
- Parity: Odd, even, mark or
- space (not used with 8-bit data)
- Stop bit: Binary 1, one or two bits
RS232 Interfacing to Microcontroller using Max 232
The RS232 interfacing using MAX232 with the microcontroller is shown below. In this, MAX 232 functions as a buffer driver for the processor. It gets the usual logic values of 0 & 5 volts and adjusts them to the RS232 typical values of +10 and -10v. Some types of microcontrollers are built in serial ports which allow for direct connection with the RS232 serial port of the computer. But, several microcontrollers give a 0-5 volts output and require a middle buffer to change the volts from 0-5v to +10 & -10 volts necessary by the RS232.
The IC MAX232 includes of a Tx-Rx arrangement so that two serial ports can be associated using the IC. Five Capacitors and each 1 microFarad are used to produce the required RS232 voltage from the TTL/CMOS voltage. The transmitter segment converts the TTL level to RS232 level, and the receiver segment gets the RS232 input and changes them to TTL level.
Basically, the transmitter pins of this IC are connected to the microcontroller. The input of the Tx pin gets TTL input from the microcontroller and the output of the Tx pin supply output to the RS232 port. The Rx pins connect to the RS 232 port such that the input of the RX receives RS232 input from the PC port, the o/p receiver pin supplies the TTL input to the microcontroller. So, the Tx gets the input from the microcontroller and provides output to the RS232 port while the Rx gets input from the RS232 port and provides output to the microcontroller.
The remaining pins are associated to the five electrolyte capacitors such that one of the capacitor is used as a voltage doublers to obtain +10V from 5V and an additional capacitor is used as a voltage inverter to get -10v. The residual three capacitors are used as bypass capacitors for V+, V- & Vcc. Thus, the capacitors operate as a voltage regulator. The main benefit of MAX 23 is, it works with 5v that allows for a single 5v supply to be used for mutually the microcontroller and the IC (integrated circuit).
Applications of RS232
The applications of RS232 Serial Communication include the following
- DNC for CNC
- Receipt Printer, POS
- PLC control
- Sensor Data Com.
- Robot, etc.
The standard feature of a PC is RS232 because; it is used to connect the printers, modems, data storage, etc. Though, there are several new growths but RS232 still find its application. The main reason is the simplicity of the standard. It lets user to communicate straight with serial ports. There are fields such as automation, laboratory, surveying who have continued the demand for RS232 due to use of very exclusive but aging equipments.
It is far cheaper to use RS232 than change the modern automation devices like CNC equipments, servo drivers, etc. are programmable by RS232. Serial ports by RS232 are used to communicate to headless system like a server where no keyboard is mounted during boot. Some embedded systems employ RS232 serial port to communicate as an another network mode monitoring.
Thus, this is all about tutorial on RS232 Serial Communication and serial interface. We hope that you have got a better understanding of this concept. Furthermore, any queries regarding this concept or to implement any communication projects please give your feedback by commenting in the comment section below. Here is a question for you, what is the function of RS232?