Digital Logical Circuit（俞鹤伟）chapter6-a.pptVIP

* * Digital Logic Chapter6 - Combinational logic design practices * OUTLINE 6.1 Documentation Standards 6.2 Circuit Timing 6.3 Combinational PLDs 6.4~6.11 Combinational Logic Building Blocks 6.1 Documentation Standards Good documentation is essential for correct design and efficient maintenance of digital systems. A documentation package should generally contain at least the following items: Specification To describes exactly what the circuit or system is supposed to do, including a description of all inputs and outputs. A schematic diagram is a formal specification of the electrical components of the system, their interconnections, and all of the details needed to construct the system. 6.1 Documentation Standards Schematic diagram Timing diagram Block diagram To show the values of logic signals as a function of time. An informal pictorial description of the system’s major functional modules and their basic inter-connections. To describe the internal function of a PLD, FPGA, or ASIC. It is normally written in HDL. 6.1 Documentation Standards It is a text document that, in conjunction with the other documentation, explains how the circuit works internally. Structured logic device description Circuit description To show the inputs, outputs, functional modules, internal data paths, and important control signals of a system. 6.1.1 Block Diagrams 6.1.2 Gate Symbols Each signal name should have an active level associated with it. Active high: A signal is active high if it performs the named action or denotes the named condition when it is HIGH or 1. Active low: 6.1.3 Signal Names and Active Levels Asserted: when a signal is at its active level. Negated/Deasserted: when it is not at its active level. Active levels may be associated with the input and output pins of gates and larger-scale logic elements. We use an inversion bubble to indicate an active-low pin and the absence of a bubble to indicate an active-high pin. 6.1.4