Hardware description languages

You: topic of conversation - hardware description languages

Losh@dka: Once you have mastered one, you can quickly learn another if necessary. The following chapters show the hardware in both schematic form and HDL model form. If you choose to skip this chapter and not learn languages ​​for describing digital hardware, you can still grasp the principles of microprocessor architecture at the circuit level. However, the vast majority of commercial systems are now built using digital hardware description languages, rather than at the circuitry level. If you ever plan to design digital circuits in your career, we strongly recommend that you learn one of the hardware description languages.

You: Verilog schema description language

Losh@dka: Example 4.31 MUR AUTOMATIC FOR PATTERN RECOGNITION

SystemVerilog module patternMoore(input logic clk, input logic reset, input logic a, output logic y);

typedef enum logic [1:0] {S0, S1, S2} statetype;

statetype state, nextstate; // state register always_ff

@(posedge clk, posedge reset)

if (reset) state <= S0;

else state <= nextstate; // next state logic always_comb

case (state)

S0: if (a) nextstate = S0; else nextstate = S1;

S1: if (a) nextstate = S2; else nextstate = S1;

S2: if (a) nextstate = S0; else nextstate = S1;

default: nextstate = S0;

endcase

output logic assign y = (state = = S2);

endmodule

Note that non-blocking assignments (<=) are used in the status register to describe sequential logic, and blocking assignments (=) are used for combinational logic of the next state.

VHDL library IEEE;

use IEEE. STD_LOGIC_1164. all;

entity patternMoore is port(clk, reset: in STD_LOGIC; a: in STD_LOGIC; y: out STD_LOGIC); end;

architecture synth of patternMoore is type statetype is (S0, S1, S2);

signal state, nextstate: statetype;

begin

–– state register process(clk, reset)

begin

if reset then state <= S0;

elsif rising_edge(clk) then state <= nextstate;

end if;

end process;

–– next state logic process(all)

begin

case state is when S0 => if a then nextstate <= S0;

else nextstate <= S1; end if;

when S1 => if a then nextstate <= S2; else nextstate <= S1; end if;

when S2 => if a then nextstate <= S0; else nextstate <= S1; end if;

when others => nextstate <= S0;

end case;

end process;

––output logic

y <= ‘1’

when state = S2 else ‘0’;

end;

You: How Verilog VHDL Circuit Compiles to Silicon on Transistors

Losh@dka: A compiler is a program that translates text written in high-level language into its low-level representation: assembly language or machine code. In other words, the compiler reads a file with a C program and converts it into a file with executable code. There is a huge amount of literature on compilers, so here we will limit ourselves to only a brief introduction. The compiler's work can be broken down into several steps: (1) preprocessing, during which declarations from libraries are included in the program and macro substitution is performed; (2) removing all unused information for code generation, such as comments; (3) translation of high-level language operators into their corresponding sets of machine instructions; (4) assembling all files with machine instructions, as well as library functions, into a single executable file. Each processor uses its own set of instructions, so the program must be compiled for the exact processor on which it will run.

The "foundation" from which the construction of MOSFETs begins is a thin round silicon wafer (wafer) from about 15 cm to 30 cm in diameter, in the Russian-language literature called a substrate, wafer or wafer. The manufacturing process begins with a blank substrate. This process involves a predetermined sequence of operations in which impurities are implanted into silicon, thin films of silicon and silicon dioxide are grown on a substrate, and a metal layer is deposited. After each operation, a certain pattern is applied to the substrate as a mask, so that the material applied during the next operation remains only in those places where it is needed. Since the dimensions of a single transistor are fractions of a micron, and the entire substrate is processed in a single manufacturing process, when billions of transistors are simultaneously produced, the cost of one transistor is significantly reduced. ; - {

29 shows a schematic cross-section of each of these two types of transistors, as if we had cut the crystal and are now looking at the transistor from the side. In n-type transistors, called n-MOSFETs, the areas where n-type semiconductor impurities are located - in turn called the source and drain - are located near the gate (gate), and this entire structure is placed on the substrate p-type. In p-MOS transistors, both source and drain are p-type regions located on an n-type substrate. The MOSFET behaves like a switch controlled by the voltage applied to it. In such a transistor, the junction voltage creates an electric field that turns on or off the communication line between the source and drain. : -E

A transistor is a switch with two positions "on" and "off", controlled by applying voltage or current to the control terminal. There are two main types of transistors - bipolar junction transistors and MOSFETs - metal-oxide-semiconductor-transistors (sometimes referred to as metal-oxide-semiconductor field effect transistors, or MOSFETs). In 1958, Jack Kilby of Texas Instruments created the first integrated circuit with two transistors. In 1959, Robert Noyce, then at Fairchild Semiconductor, patented a method for connecting multiple transistors on a single silicon chip. At that time, one transistor cost about $ 10. ; -}

You: that is, logic gates are built on transistors?

Losh@dka: The choice of VDD and logic levels can be arbitrary, but this choice should ensure compatibility of all logic gates communicating within the same digital system. Therefore, gates are usually grouped into logic families in such a way that any element from one family, when combined with any other element from the same family, automatically enforces the principle of static discipline. Logic gates of the same family connect to each other as easily as Lego blocks, because they are fully compatible in power supply voltage and logic levels. Four main families of logic gates dominated from the 70s to the 90s of the last century - TTL - Transistor-Transistor Logic (TTL), CMOS - logic built on a complementary structure of metal-oxide-semiconductor (Complementary Metal-Oxide-Semiconductor Logic, or CMOS), NTTL - Low-Voltage Transistor-Transistor Logic (LVTTL), and Low-Voltage Complementary Metal-Oxide (Low-Voltage Complementary Metal-Oxide) low-voltage logic on the complementary metal-oxide-semiconductor - Semiconductor Logic, or LVCMOS). Logic levels for all these families are presented in Tab.

When using pseudo-nMOS logic (pseudo-nMOS logic), or simply pseudo-logic, the slow stack of p-MOS transistors is replaced with one "weak" p-MOS transistor, which is always on. Such a transistor is often referred to as a weak pull-up transistor. The physical parameters of the p-MOS transistor are selected in such a way that this transistor to a high logic level (1) the output Y "pulls up weakly" - that is, only when all n-MOS transistors are turned off. But if at the same time at least one of the n-MOS transistors turns on, then, surpassing the weak pull-up transistor in power, it "pulls" the Y output so close to the GND ground voltage that the output is a logic 0.

You: Thanks for the interview, Losh@dka!