RS 232 & MAX 232

RS 232 & MAX 232

RS 232 (Recommended Standard 232) is the serial communication protocol (Protocol= set of rules), generally used to connect computer CPU to its different peripherals like monitor, printer etc. RS232 which has 9 pins also referred as DB9 connector. Here are some images of RS232

 Fig 1: Male RS 232 connector (Zoom it to see pin numbers inside)

 

Fig 2: Pin out of RS232

Fig 2: Actual RS 232 cable

Fig 4: Female RS 232 connector

Let’s see the pin details of RS232

Pin No.	Pin Name	Full form/ acronym	Function
1	DCD\	Data carrier detect	Output signal from the modem (DTE) and input to the PC (DTE).
2	RxD	Receive data	Receive data serially
3	TxD	Transmit data	Transmit data serially
4	DTR\	Data terminal ready	Active low signal used to inform the modem that the computer is working proper
5	GND	Ground	Ground
6	DSR\	Data set ready	Active low signal and activated if there is proper communication between modem and telephone
7	RTS\	Request to send	Active low output from the Data Terminal  Equipment (DTE)/computer to the modem
8	CTS\	Clear to send	Input signal to the DTE is used by the DTE to start transmission.
9	RI	Ring indicator	Output from the modem (DCE) and an input to a PC (DTE)

Note:   DTE = Data Terminal Equipment = PC

            DCE = Data Communication Equipment = Modem

 

MAX 232 :

For communication between microcontroller development board and computer, RS 232 is used which is followed by MAX 232 IC. MAX 232 is bi-directional voltage converter and used to convert voltage level.

RS232 represents logic “1” as -3v to -25v where logic “0” as +3v to +25v which make -3v to +3v undefined. To cope up with this situation RS 232 voltage levels need to be converted into microcontroller’s voltage levels. MAX 232 is the IC which does the same. 

Fig 5: MAX 232

The MAX232 consists of two sets of line drivers. One set i.e. T1 & T2 is used for transferring of data and other set i.e. R1 & R2 is used for receiving data. T1 in pin is the TTL side and is connected to T x D of microcontroller. T1out is the RS232 side that is connected to R x D pin of RS232 DB. The R1in is the RS232 side that is connected to the T x D pin of RS232 DB connector and R1out is TTL side that is connected to the R x D pin of the microcontroller. MAX 232 uses four capacitors whose values are ranging from 1 to 22uF.