DAC R-2R Ladder circuit

Visual Basic uses the Microsoft Comm Control 6.0 (MSComm) component for serial interfacing. One MSComm is used for just one serial port. If we use more than one serial port, we must use as many MSComms as Serial port.

MSComm properties

 The Properties of the Mscomm1 are selected as shown in the properties windows below:

There are two codes (in computer and AT89S51) for testing communication between computer and AT89S51.

Hardware properties:

• Frequency oscillator in AT89S51 circuit is 11.0592 MHz
• Baudrate = 9600 bps
• Port PC = com1

Within a computer data is transferred in parallel, because that is the fastest way to do it. For transferring data over long distances, however, parallel data transmission requires to many wires. Therefore, data to be sent long distances is usually converted from parallel form to serial form so that it can be sent on a single wire or pair of wires. Serial data received from a distant source is converted to parallel form so that it can easily be transferred on the computer buses. Three terms often encountered in literature on serial data systems are simplex, half-duplex and full-duplex. A simplex data line can transmit data only in one direction. Half-duplex transmission means that communications can take place in either direction between two systems, but can only occur in one direction at a time. The term full-duplex means that each system can send and receive data at the same time.