Serial Port.

Serial Port.

The example presented here shows a serial port - connected to a modem - which follows the standard RS-232.

1 - Pins 1 and 5 of the computer port to connect respectively to pins 8 and 7 from the modem port. Pins 1 and 8
share the same ground connection. 5:07 The pins allow the PC to detect a signal from the telephone line.

2 - Pin 6 - the same on both sides - it sends a signal indicating that data is ready to be sent.

3 - Pin 4 PC connects to pin 20 of the modem. It signals that the PC is ready to receive data.

4 - Pin 7 PC connects to pin 4 of the modem. He makes a request to send data.

5 - 8 pin PC sends a signal to pin 5 of the modem when the PC is ready to receive data.

6 - Pin 2 PC sends data to the modem pin 3. Only one bit - here exemplified as a hub for bit blue
1 and a red ball in bit 0 - the cable can pass at a time. The fact that the data is sent serially, gives
name to such connection.

7 - Pin 3 PC receives data from the modem pin 2. Again, the bits can move by only one cable at a time.

8 - 9 pin PC conccta up to pin 22 of the modem to detect the phone ringing.

Source: Evolution of Computers