Serial Port RS232 for bus protocol

1 logic level

EIA-RS-232C of electrical properties, logic and various signal line functions are defined.

On txd and rxd:

Logic 1 (Mark) =-3v ~ -15 V

Logic 0 (Space) = + 3 ~ + 15 V

On the control line such as RTS, CTS, DSR, DTR, and DCD:

Effective Signal (on, positive voltage) = + 3v ~ + 15 V

Invalid signal (disconnected, off, negative voltage) =-3v ~ -15 V

 

2. Pin Definition

Pin definition symbol

1 Carrier Detection DCD Pin 1 received Line Signal Detector (data carrier detect)

2 receive data rxd pin 2 received ed data

3 send data txd Pin 3 transmit data

4 data terminal prepare DTR pin 4 Data Terminal ready

5 Signal Location SG pin 5 signal ground

6. Data preparation: DSR Pin 6 data set ready

7. Send the RTS pin 7 request to send

8 clear send CTS pin 8 clear to send

9. When the ringing tone is set to RI pin 9 ring indicator

 

3. ing between 9-pin and 25-pin serial port pins

 

4 connection method

 

Usually not.While the normal PC hardware might well run with just Tx, RX and ground connected, most driver software will wait forever for one of the handshaking lines to go to the correct level. depending on the signal state it might sometimes work, other times it might not. the reliable solution is to loop back the handshake lines if they are not used.

Handshake looping a PC serial Connector

 

Http://airborn.com.au/serial/rs232.html

 

5 serial RS232 data frame format

On the bus of the serial port, the high level is the default level. When a frame of data starts to be transmitted, the bus must be dropped to one position as the start position.