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3.The DBdirective is designed to allocate byte sized (8 bit) quantities like characters and register halves. It has the special property of being able to allocate strings as well. Elements of the string may be numbers, characters, or quoted strings, separated by commas.

 

9.Describe the apparatus organization of interrupts. Describe the service of interrupt procedure.

Which categories (groups) of units (from the point of view of addressing) are connected to the system bus? How is solved the problem of identification and division of these units?

How the processor can address a segment that is aligned on a byte, word, or double word boundary?

What problems does the TD allow to solve? Which modes of program execution (debugging) are used in the TD?

What is Memory Model? Describe Tiny and Small types of Memory models.

The concept of Model of Memory was used first for programming in C, but it has turned out that it may be successfully used in Assembly as well. The Model of Memory started to support by Assembly translators beginning from TASM-3x. In these connection simplified directives of segmentation were introduced. Along with the simplified directives of segmentation the directive MODEL, which manages the segments allocation and substitutes directive ASSUME, is used.

Model of Memory (used by a program in Assembly) determines a number of segments, segments allocation in the memory, dimensions and properties of some variables used in the program, on default, it determines types of procedures (far or near) and so on.

 

There are 7 types of Memory Model:

· Tiny; Small; Medium; Compact; Large; Huge; Flat.

1. In the Tiny Model only one segment (name “DGROUP”) is used, so registers CS,DS and SS have got the same predestination. Such model corresponds programs, which are stored in files of *.com type. The maximal length of such program can not be more than 64 Kbytes.

2. In the Small Model there are 2 segments: segment of codes and data segment (name “DGROUP”); DS and SS registers have got the similar predestination. This type is more often used.

3. The Compact Model is analogous to the Small, but it permits to use several data segments, DS and SS registers have got the similar predestination.



4. The Medium Model may be considered in some sense as opposite to the Compact one, since in such programs several segments of codes and one common segment of data (stack is also included in this segment) are used. An access to subroutines of these programs is fulfilled with help of far addresses (segment:offset), and to data by using only offset (near addresses).

Formulate the Rule of recording multi-bytes numbers in Intel microprocessors (“little endian” method); give an example.

What is Structure? Describe stages of using structures in a program. What is Record? Describe stages of using records in a program.

Structure is a type of data, which consists of fixed number of elements of different characteristics.

Structures can be considered as pictures with descriptions of data formats, which may be patched (наложены) on different areas of memory with a purpose – to have a possibility for addressing to fields of these areas with help of mnemonic names, which are determined in the structure description.

Structures are especially useful in cases, when it is necessary to address for memory areas, which haven’t been included in program’s segments (i.e. to such fields, which are not possible to describe with help of symbolic names). Structures are also used in such situations, when a program includes complex collections of data, which repeat many times and have different meanings.



For using structures in the program, it is necessary:

1. To set a picture of the structure, i.e. to determine a new type of data, which will be used in future for determination of variables of this type;

2. To determine an exemplar of the structure, i.e. to initialize a certain variable with the beforehand determined (with help of the picture) structure;

3. To organize access (addressing) to this variable.

It is important to distinguish two concepts: description of structure and structure determination.

“To describe a structure” in the program means, that a scheme or a picture is to be pointed out; in this case the memory will not be allotted. The picture (or the scheme) may be considered only as information for the translator: how the fields will be located, and what are their meanings on default.

“To determine a structure” means pointing out to the translator to allot the memory and give a certain name for the allotted part of memory.

Structure may be described only once, but it can be determined many times.

The description of a structure has got the following syntax:

name_of_structure STRUC

<description of fields>


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