SIMPLE GATES

This section describes the generic bused gate functions of LogiBLOX. Bused gate functions are defined as generalizations of the common logic primitives: AND, INVERT, NAND, NOR, OR, XNOR, and XOR. Except for the INVERT function, each of these can be implemented in three different ways, depending on the number and type of inputs.

Figure 4.32 The Simple Gates Module

The following functions are described for the AND gate, but the same bus expansion criteria apply to the other functions.

Type 1 AND gate: O = A₀ • A₁ •…• A_(n-1)

Figure 4.33 Type 1 AND Gate: Symbol and Logic Diagram

Type 2 AND gate: O_n = A • B_n

Figure 4.34 Type 2 AND Gate: Symbol and Logic Diagram

Type 3 AND gate: O_n = A_n • B_n

Figure 4.35 Type 3 AND Gate: Symbol and Logic Diagram

You can use the inversions of these logic functions by connecting an INVERT module to the outputs. You can also invert individual inputs (active Low) by using the Inversion Mask attribute associated with each module or specify which individual inputs will be active High with the Decode Mask attribute. See the “Inverting and Decoding Masks for Gated Modules” section of the “Understanding Attributes” chapter for more information.

INVERT gate: O_n = !A_n

Figure 4.36 INVERT gate: Symbol and Logic Diagram

Attributes

To select the type of logic, click on the radio button located under the type of logic you want. The following descriptions use the AND module for an example, but the logic applies to all of the Simple Gates modules except the INVERT module.

• Type_1 (One input bus): The Type 1 AND module logically ANDs the individual signals of an input bus of width (n) to produce a single output signal, where (n) varies from 2-64 bits.
  
  
• Type_2 (One input net and one input bus): The Type 2 AND module logically ANDs the individual signals of an input bus of width (n) with a single input to produce an output bus of width (n), where (n) varies from 2-64 bits.
  
  
• Type_3 (2-8 input buses): The Type 3 AND module logically ANDs (m) input buses of width (n), where (m) varies from 2-8 buses and (n) varies from 2-64 bits. The output is a single bus of width (n).
  
  

Usage: This attribute does not apply to the INVERT module.

Use this attribute to select the type of gate: AND, INVERT, NAND, NOR, OR, XNOR, or XOR.

Specifies the number of Input buses (m) of the module.

Usage: This attribute applies to Type 3 modules only. Its value must be in the range 2-8.

Style defines the implementation style (area or speed preference).

Usage: This attribute does not apply to the INVERT module. For more information, see the “Implementation Styles” section of the “Understanding Attributes” chapter.

A High level on this attribute inverts the input of the gate. See the “Inverting and Decoding Masks for Gated Modules” section of the “Understanding Attributes” chapter for more information.

Usage: This attribute does not apply to Type 3 modules.

A Low level on this attribute inverts the input value. See the “Inverting and Decoding Masks for Gated Modules” section of the “Understanding Attributes” chapter for more information.

Usage: This attribute does not apply to Type 3 modules.