Intel Microprocessor

- The 8279 is basically a programmable keyboard and a component for display interfacing.

- The 8279 can scan and also encode a 64 key keyboard as well as a numerical display of 16 digits.

- The keyboard has a buffer based on FIFO to store up to 8 keys after which the processor must retrieve a character.

- It contains 8 lines that can be used to connect to 8 columns of a keyboard. There are two additional lines for STB keys.

- Once a key is pressed they are automatically debounced and it can function using two modes -key lockout and n-key roller.

- On simultaneous presses only the first key is detected. In case of n-key rollover mode all simultaneous presses are detected and stored in the internal buffer.

- Internal Data Bus: As its name suggests the internal data bus only works inside a CPU that is internally. It is able to communicate with the internal cache memories of

the CPU. Since they are internally placed they are relatively quick and are now affected by the rest of the computer.

- External Data bus: This type of bus is used to connect and interface the computer to its connected peripheral devices. Since they are external and do not lie within the

circuitry of the cpu they are relatively slower.

- The 8088 processor in itself contains a 16-bit internal data bus coupled with a 20-bit address register. This allows the processor to address to a maximum of 1 MB

memory.

VESA stands for Video Electronics Standards Association. It is used for the transmission of high speed input-output operations as well as to directly access the

memory.

- It comprises of a various videos card and monitor manufacturers , they creates standards to define the resolution, number of colors, and other display properties.

- In this way graphics cards have direct access to the processor and system memory. It does not suffer from limitations of the ISA bus.

Some of the cons of using VESA are as follows:

- VESA suffers from interoperability issues.

- VESA Standard is also unreliable as there are multiple cases in which the hardware such as the monitor or the card to display are unstable and buggy.

- Highly dependent on the hardware configuration, getting the right combination is generally difficult.

- VLB cards are not easy to install / service.

The characteristics of CGA are as follows:

- The CGA or the Color/Graphics adapter was the first color graphics card for IBM pc`s.

- It contain 16KB of video memory and used an Rca jack to connect to a Tv or monitor ( NTSC compatible).

- It could also be connected to a RBGI interface CRT monitor (4-bit).

The characteristics of VGA graphics are as follows:

- The VGA or the video graphics array was a hardware introduced with the IMB PS/2 computers.

- It has been widely adopted world over and now actually implies the analog computer display standard.

- Eventually after much modifications by other manufacturers the VGA was superseded by SVGA.

- Macro can be considered to be a sequence of instructions to which a name is assigned.

- For short sequence of instructions which are of fixed nature Macros are used.

- They can execute faster as compared to subroutines.

- The MACRO directives are used to inform the assembler the starting of a macro.

- In order to enclose a macro the ENDM directive is used.

- The general format of the MACRO directive is :

Macro Name MACRO ARG1, ARG2 , …..,ARG N.

- To create macro sequences conditional assembly language statements are used. Theses statements control the flow of the program and are variations of the IF-THEN, IF-THEN-ELSE, DO-WHILE, and REPEAT-UNTIL constructs used in high-level language programming languages.

In developing a Microprocessor based computer system the following steps are involved:

- The first step is to develop the CPU module.By doing so the basic system timing, sequential startup order is established.

- After that memory needs to be added: The primary memory is essential for the programs that are stored on the computer. There can be several forms of memories

with different hierarchies. The CPU loads and fetches instruction from the memory.

- The third step is adding input/output: There are basically two hardware techniques for getting data into and out of a computer.

i. The parallel interface is the most common and natural form.

ii. The serial interface is the second technique

- Debugger: As its name suggests the debugger is used to test and debug programs. The debugger allows a user to test a program step by step, so that the problem points or steps can be identified and rectified. It allows the user to inspect the registers and the memory locations after a program has executed.

- Assembler: The assembler is used to convert assembly language written by a user or a program into a machine recognizable format.

- Linker: There are certain programs which are large in size and cannot be executed at one go simultaneously. Such programs are divided into subprograms also known as modules. The linker is used to link such small programs to form one large program.

The following are the modes of operation of the programmable timer 8254:

- Mode 0: Also known as the interrupt on terminal count. In this mode the output is initially low. Once the count of terminal is reached the output becomes high.

- Mode 1: Programmable one shot is also known as the hardware triggered one-shot. For it to happen, the count registers must be loaded and the A 0-1 pulse has to be sent to the Gate input in order to trigger the counter.

- Mode 2: Rate generator, this process is repeated indefinitely.

- Mode 3: Square wave generator, when gate=1, The out is a square wave where the high pulse is equal to the low pulse of N is an even number. In case the N is an odd number the high pulse is longer. The mode-3 is commonly used for as frequency divider.

The various types of addressing modes for microprocessors are as follows:

- Direct Mode: In this mode of addressing the instruction in itself includes memory access. This can be accessed by the CPU directly.

- Indirect Mode: In this type of addressing the address which has been specified within the instruction contains the address of the operands.

- Register direct and indirect modes: In this mode as the name suggests no addresses are specified in this mode instead registers are specified.

- Immediate Mode: In this type of addressing mode the operand itself is the data.

- Relative Mode: In this mode the operand specified in the instruction is an offset address and not the actual address.

- CWD also known as the Convert signed Word to signed Double word instruction, it is used to extend the sign bit of a word in AX register to all the bits of the DX register. Generally used before a signed word in AX. Then it is divided by another signed word using IDIV instruction. It does not affect any flag.

- LOOP: (Jump to specified label until CX = 0): As the name suggests the loop instruction is used to repeat a sequence of instructions for a specified number of time. It does not affect any flag and the number of times the loop is to be repeated is stored in the CX register.

- IMUL: This instruction is used for the multiplication of two signed numbers.The result of imul between two signed numbers is signed as well. The OF (Over flow) and CF (Carry flag) flags get affected by this instruction.

- SAR: Also known as Shift each bit of operand right, this instruction shifts each bit of the operand in a register or memory location, right by the number of bits specified. The carry flag is affected by this operation.