Introduction to RS232

1. Introduction

RS232 is a standard for serial communication transmission of data between different devices. It is one of the oldest interface standards used in computing and was first introduced in the 1960s. RS232 has been widely used for connecting devices such as printers, modems, and other peripherals to computers. Despite the advent of newer interface standards, RS232 is still used in many industrial and commercial applications today.

2. What is RS232

RS232 is a serial communication standard that uses a single wire for transmitting data from one device to another. It uses a voltage level shift to distinguish between bits and bytes of data. The voltage levels for RS232 are typically defined as +15 volts and -15 volts, with positive voltage representing logic 0 and negative voltage representing logic 1. The data is transmitted in a bit-by-bit manner, with the start bit, data bits, parity bit, and stop bit forming a single byte.

3. Hardware Specification and Connections

The hardware specification of RS-232 defines the electrical characteristics of the signals used for communication. The max speed at which the data can be transmitted is 115200.the main types of connectors that are used are DB-25 and DB-9. The DB-25 contains 25 pins which are use for data transmission and receiving (may not all pins are used) similarly the DB-9 have 99 pins. These ports are of two types: male connector (DTE) & female connector (DCE). It is also known as D-type connector.

4. RS232 Packet Structure

RS232 specifies the electrical, mechanical, and timing characteristics of the serial communication between devices, including the use of a UART packet format for transmitting data. This packet format includes a start bit, data bits, an optional parity bit, and stop bits, which is also commonly used in UART communication.

RS232 uses voltage levels to represent binary data, with a logical 0 represented by a positive voltage and a logical 1 represented by a negative voltage. The voltage levels are specified to ensure reliable communication over relatively long distances, up to 50 feet or more.

5. RS232 HandShake

In RS-232 communication, the term handshake pertains to the procedure where two devices acknowledge each other's availability and willingness to exchange data. This process guarantees that both devices are equipped and prepared to transmit and receive data, which helps prevent any loss or damage to the information being transmitted.

The most common handshake signals used in RS-232 communication are the Request to Send (RTS) and Clear to Send (CTS) signals. When a device is ready to send data, it sends an RTS signal to the receiving device, indicating that it is requesting permission to transmit. The receiving device responds with a CTS signal, indicating that it is ready to receive data. Once the transmitting device receives the CTS signal, it can begin transmitting data.

In addition to the Request to Send (RTS) and Clear to Send (CTS) signals, there are other handshake signals used in RS-232 communication. The Data Terminal Ready (DTR) and Data Set Ready (DSR) signals indicate that the connected devices are ready for communication. The Carrier Detect (CD) signal is used to indicate that the receiving device is detecting a carrier signal from the transmitting device. Once the data transmission has started, the Data Carrier Detect (DCD) signal is used to indicate that the transmission is in progress.

These handshake signals play a crucial role in ensuring reliable communication in RS-232 networks, especially when data integrity is critical. By using these signals, devices can confirm that they are ready to communicate and that data transmission has started or is ongoing.

6. MAX-RS232 IC

The MAX232 is a type of IC that is commonly used in serial communication applications. It is specifically designed to convert the RS232 voltage levels (-15V to +15V) to TTL voltage levels (0V to +5V) and vice versa.

Inside the MAX232 IC, there are two pairs of drivers and receivers, each containing two channels. The drivers use charge pumps to produce the required RS232 voltage levels, whereas the receivers employ voltage dividers to transform the RS232 levels back to TTL levels. In addition to this, the MAX232 includes capacitors for charge pump voltage doubling and an internal oscillator that generates the necessary timing signals for data transmission. The IC typically requires external capacitors to stabilize the charge pump and voltage regulators to ensure a stable power supply.

7. Applications of RS232

RS232 has been used extensively in the past for connecting devices such as printers, modems, and other peripherals to computers. It has also been used in industrial and commercial applications such as data acquisition and control, process control systems, and factory automation. RS232 is still used in many industrial and commercial applications today, despite the advent of newer interface standards such as USB and Ethernet.

8. Conclusion

RS232 is a standard for serial communication transmission of data between different devices. It has been widely used in the past for connecting devices such as printers, modems, and other peripherals to computers, and is still used in many industrial and commercial applications today. RS232 is a simple and reliable communication standard that has stood the test of time, and will likely continue to be used for many years to come.