Explanation: SIGNED and UNSIGNED data types are defined in the std_logic_arith package of the IEEE library. These data types are mainly intended for arithmetic operations. This is why they are defined in the arithmetic package.

Explanation: Unlike BIT and STD_LOGIC types; SIGNED and UNSIGNED follow the syntax similar to BIT_VECTOR and STD_LOGIC_VECTOR. Also, IN and OUT are just to specify the direction of signal.

Explanation: In SIGNED and UNSIGNED, SIGN word refers to the positive or negative sign of any number. UNSIGNED data type has no sign and therefore, it is always positive. Therefore, an UNSIGNED number will be always greater than zero.

Explanation: x is declared as an UNSIGNED data type. Therefore, all the 4 bits will be data bits and it will be positive. So, converting 1101 in decimal, we get 1101 equivalent to 14 in decimal number system.

Explanation: Signed numbers always have first bit representing the sign of the number which is one for the negative and zero for the positive. Also, signed number is represented in 2’s complement form. Therefore, the given number is -3.

Explanation: SIGNED and UNSIGNED data types are intended for arithmetic operations mainly and using logical operators with these data types is illegal. Therefore, only option x <= a + b; y <= a – b; is completely legal. In all other options there are logical operations so those can’t be considered as legal.

Explanation: Unlike SIGNED and UNSIGNED, STD_LOGIC_VECTOR data type is used mainly for logical operations and we can’t use arithmetic operations with STD_LOGIC_VECTOR. Also, && is not the sign for any operation in VHDL, if you want to perform and operation, then you have to write AND not &&.

Explanation: Physical type is used for representing physical values such as time, voltage, etc. by using some base unit. Physical quantities are used in various digital systems and these are important for modelling such systems. Integer and Real are the data types for numbers and there is no data type called Imaginary.

Explanation: Base unit is the smallest possible unit for any physical literal by using which we can derive all other units of the same literal. For example, in case of TIME, the base unit is nanosecond. We can create any bigger unit by using nanoseconds. For example 1 microsecond = 1000 nanosecond.

Explanation: TIME is the only predefined physical data type in VHDL. The base unit of TIME is nanosecond. TIME literal is defined in the standard package of std library.

Explanation: Units nanosecond (ns) written after the number shows that it is of type TIME and VHDL doesn’t allow TIME type to be assigned to a real Signal. So option d is illegal.

Explanation: Multidimensional arrays can be seen as array of arrays. For example, we need to implement ROM of 512×4 then we need to define a 2 dimensional array with 4 columns and 512 rows. So, memories can be defined by using 2D array. In which one dimension can show the size of memory and another can show the width of one word.

Explanation: As in C, Structures are used to collect different data types under a common name. Similarly, RECORD type in VHDL is used for collecting different data types and objects in a single object.

Explanation: SIGNALs are used to pass information between entities, they act as interconnection between different entities whereas VARIABLEs can be used in the process or subprogram in which it is declared. So, VARIABLEs are local to the block in which they are declared.

Explanation: Access types are used to hold an address of some object which is quite similar to pointers in traditional programming languages. By using the address stored in Access data type, we can access another data objects similar to pointers.