# Summary.

In this section we identified key features common to all programmable systems and then illustrated the basic principles, of the electronic devices and circuits that provide these features. This did introduce some advanced topics, such as binary arithmetic and address decoding, however the aim at this stage, is just to introduce these concepts and their role in computer systems. The objectives for this section are listed below.

• Recall some of the basic principles on which the abilities of computer systems are based, i.e.
• Using numeric codes to store information.
• Using digital logic circuits to make basic decisions.
• The principle of programmability where the operation of a microprocessor is changed by "feeding" it different instruction codes.
• Recall that we use binary numbers in computing, because the devices that digital systems are based on, only have two states they can be set to and therefore they can only represent digits 0 and 1.
• Recall that a digital logic circuit called a latch, can be set or reset to provide a 1 bit memory and that a series of these circuits can be used to store binary codes.
• Recall that;
• A digital logic circuit can be built to add two binary digits (along with any "carry in" that resulted from the addition of a previous pair of binary digits). The circuit can also carry over bits to a subsequent stage.
• By linking these circuits together we can perform addition on binary numbers.
• By using techniques of binary mathematics the circuit can also perform subtraction multiplication and division.
• Recall that address decoding involves using digital circuits, to enable the microprocessor to select the memory location it wants to communicate with.
• Understand the roles of the data, control and address buses in a digital circuit.
• Understand the boot process, as the automatic transmission of a sequence of instructions, to program the microprocessor to control the system.
• Recall that devices such as printers, monitors and keyboards are connected to the system via input output ports and that they can send IRQs to the microprocessor, to "request" it to interact with the device.