The RS232 connector is a port for data exchange between devices. It is designed for data exchange between DTE (data terminal equipment) or PC and DCE (data communication equipment) or MODEM.
What is RS232 connector
The need for RS232 comes from the limitations imposed by parallel data exchange. RS232 uses serial communication protocol, in which the data exchange is done little by little. Although RS232 was later replaced with a faster USB (Universal Serial Bus), it is still popular in some areas. RS232 used to have 25 pins, but it is now reduced to only 9 pins.
RS232 Pinout &Configuration
RS232 has nine terminals, as shown in the table.
|Pin Number||Pin Name||Description|
|DATA pins (Data flow takes through these pins)|
|2||RXD||Receive Data (Data is received though this pin)|
|3||TXD||Transmit Data (Data is transmitted through this pin)|
|CONTROL pins (These pins are for establishing interface and to avoid data loss)|
|1||CD||Carrier Detect(Set by MODEM when answer is received by remote MODEM )|
|4||DTR||Data Terminal Ready(Set by PC to prepare MODEM to be connected to telephone circuit)|
|6||DSR||Data Set Ready(Set by MODEM to tell PC it is ready to receive and send data)|
|7||RTS||Request To Send(Set by PC to tell MODEM that MODEM can begin sending data)|
|8||CTS||Clear To send(Set by MODEM to tell PC that it is ready to receive data)|
|9||RI||Set by MODEM to tell PC a ringing condition has been detected.|
|5||GND||Ground (Used as reference for all pin voltage pulses)|
- RS232 uses Asynchronous communication so no clock is shared between PC and MODEM.
- Logic ‘1’ on pin is stated by voltage of range ‘-15V to -3V’ and Logic ‘0’ on pin is stated by voltage of range ‘+3V to +15V’. The logic has wide voltage range giving convenience for user.
- MAX232 IC can be installed easily to establish RS232 interface with microcontrollers.
- Full duplex interface of RS232 is very convenient.
- Two pin simplex RS232 interface can also be established easily if required.
- A maximum data transfer speed of 19 Kbps(Kilobits per second) is possible through RS232
- A maximum current of 500mA can be drawn from pins of RS232
- The interface can be established up to a distance of 50 feet.
- No pins dedicated to power the device (no VCC)
- More communication pins
- At higher speeds, it is difficult to switch between + 15V and – 15V
- Up to 19 kbps
- Maximum distance 50 feet
- The more pins, the more noise
- Unlike I2C, only one device can be connected to the RS232 connector
- Hardware is required to convert the high voltage logic of RS232 to be compatible with TTL (controller and processor unit)
How does a RS232 connector work?
As mentioned before, we can’t connect RS232 directly to the controller, we need MAX232 IC to convert the high voltage signal to TTL, and vice versa. A typical circuit is shown below.
Here, we connect the controller to female RS232 through MAX232 converter chip. In RS232, the highest communication voltage is + 15V, and the lowest is – 15V. Voltage level cannot be used in sensitive electronic equipment, so the medium we use is MAX232. The chip converts TTL logic pulse of controller into RS232 voltage level pulse, and vice versa. Without this chip, you may permanently damage something.
Here are some common scenarios of RS232:
- When you want a simple communication interface between two units. Dual pin full duplex communication can be easily established on the RS232 port.
- RS232 is used in the system which is difficult to realize clock sharing. RS232 is asynchronous, so there is no clock sharing between systems. You only need to set the data bit rate for each unit. Once the baud rate is set, each unit will sample the data according to the set baud rate.
- RS232 is also used to control a unit, especially without delay or error.
- The RS232 interface also provides more accurate data, which is a requirement in some cases.
RS232 connector Circuit
RS232 connector Applications
- Personal Computers
- Memory devices
- Motor control units
- Printers and Scanners
- Telephone lines
- Used basically where serial data transfer is required
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