Sequential Circuits - Revizia istoricului

Cbira: /* Clock signal */

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Clock signal

Cbira: /* Clock signal */

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Clock signal

Cbira: /* Memory Circuits. Register */

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Memory Circuits. Register

Cbira: /* Memory Circuits. Register */

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Memory Circuits. Register

Cbira: /* Memory Circuits. Register */

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Memory Circuits. Register

Cbira: /* Memory Circuits. Register */

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Memory Circuits. Register

Cbira: Pagină nouă: Sequential circuits are circuits that are synchronized by a clock signal, ie whose outputs change only on the positive (or negative, clockwise) front of the clock. == Clock signal...

2018-04-11T23:15:08Z

Pagină nouă: Sequential circuits are circuits that are synchronized by a clock signal, ie whose outputs change only on the positive (or negative, clockwise) front of the clock. == Clock signal...

Pagină nouă

Sequential circuits are circuits that are synchronized by a clock signal, ie whose outputs change only on the positive (or negative, clockwise) front of the clock.

== Clock signal ==

[[File: seq0.png | thumb | Clock Sign in Modelsim]]

The clock signal is a periodic signal that oscillates with a certain frequency, called the clock frequency.

'''Note:''' See syntax [[Verilog #Test Modules (Unintelligible) | Verilog]] to find out how to generate a clock signal in simulation.

[[File: seq1.png | Clock Signal Elements]]

== Memory Circuits. Register ==

The register is the basic memory cell and the base of the sequential circuits. Once a value is loaded into a registry, it is retained until it is overwritten with another value.

<div class="rule"> <font color="red"> '''Rule:''' </font>
<div class="rule"> <font color="red"> '''Rule:''' </font> In Verilog #always sequential blocks. Non-blocking assignments | Verilog]], a value of a registry is loaded only in blocks '''always'''. </Div>
If a module is sequential, then it will have a clock input port. </div> </div> </div> <div class="rule" >

[[File: seq2.png | Graphical Representation of a Nbit Registry]]

[[File: seq3.png | thumb | Simulation of a 4-bit registry]]

This is the implementation in Verilog of a 4-bit register that only loads the register with the input value, and in the picture you can see a Modelsim simulation that shows that the output only changes on the positive clock front following the change of input:

<syntaxhighlight lang="verilog">
module Register (
output reg [3: 0] out,
input [3: 0] in,
input clock
)

always @ (posedge clock) begin
out <= in;
end

endmodule
<syntaxhighlight>

== Reset for sequential circuits ==

There are situations where registers need to be reset, that is, loaded with a default value. This reset process is typically used when the circuit blocks, for one reason or another, or when it is to be restarted from an initial state. Circuits for which it is necessary to be reset can be added to a reset signal. The description in Verilog of a 4-bit register with a reset signal, which only loads with an input value, is the following:

<syntaxhighlight lang="verilog">
module Register (
output reg [3: 0] out,
input [3: 0] in,
input clock,
input reset
)

always @ (posedge clock) begin
if (reset) begin
out <= 4'b0;
end else begin
out <= in;
end
end

endmodule
</syntaxhighlight>

This type of reset is called synchronous reset, because it is only evaluated on the clock front (synchronous with the clock). There are also cases where the reset is asynchronous, and then the active reset queue must appear in the block's list of sensitivities' 'always'''.

@@ Linia 16: / Linia 16: @@
 <div class="rule"><font color="red">'''Rule:'''</font> Loading a value into a register is performed only on an edge of the clock </div>
-<div class="rule"> <font color="red"> '''Rule:''' </font> In Verilog #always sequential blocks. Non-blocking assignments | Verilog]], a value of a registry is loaded only in blocks '''always'''. </div>
+<div class="rule"> <font color="red"> '''Rule:''' </font> In Verilog loading a value into a register is performed in '''always''' sequential blocks. </div>
-If a module is sequential, then it will have a clock input port. </div> </div> </div> <div class="rule" >
+<div class="rule"> <font color="red"> '''Rule:''' </font> If a module is sequential, then it will have a clock input port. </div>
 [[File: seq2.png | Graphical Representation of a Nbit Registry]]

@@ Linia 15: / Linia 15: @@
 The register is the basic memory cell and the base of the sequential circuits. Once a value is loaded into a registry, it is retained until it is overwritten with another value.
-<div class="rule"><font color="red">'''Regulă:'''</font> Loading a value into a register is performed only on an edge of the clock </div>
+<div class="rule"><font color="red">'''Rule:'''</font> Loading a value into a register is performed only on an edge of the clock </div>
 <div class="rule"> <font color="red"> '''Rule:''' </font> In Verilog #always sequential blocks. Non-blocking assignments | Verilog]], a value of a registry is loaded only in blocks '''always'''. </div>
 If a module is sequential, then it will have a clock input port. </div> </div> </div> <div class="rule" >

@@ Linia 7: / Linia 7: @@
 The clock signal is a periodic signal that oscillates with a certain frequency, called the clock frequency.
-'''Note:''' See syntax [[Verilog #Test Modules (Unintelligible) | Verilog_EN]] to find out how to generate a clock signal in simulation.
+'''Note:''' See syntax [[Verilog #Test Modules (Unintelligible) | Verilog]] to find out how to generate a clock signal in simulation.
 [[File: seq1.png | Clock Signal Elements]]

@@ Linia 16: / Linia 16: @@
 <div class="rule"> <font color="red"> '''Rule:''' </font>
-<div class="rule"> <font color="red"> '''Rule:''' </font> In Verilog #always sequential blocks. Non-blocking assignments | Verilog]], a value of a registry is loaded only in blocks '''always'''. </Div>
+<div class="rule"> <font color="red"> '''Rule:''' </font> In Verilog #always sequential blocks. Non-blocking assignments | Verilog]], a value of a registry is loaded only in blocks '''always'''. </div>
 If a module is sequential, then it will have a clock input port. </div> </div> </div> <div class="rule" >
@@ Linia 37: / Linia 37: @@
 endmodule
-<syntaxhighlight>
+</syntaxhighlight>
 == Reset for sequential circuits ==
@@ Linia 62: / Linia 62: @@
 </syntaxhighlight>
-This type of reset is called synchronous reset, because it is only evaluated on the clock front (synchronous with the clock). There are also cases where the reset is asynchronous, and then the active reset queue must appear in the block's list of sensitivities' 'always'''.
+This type of reset is called synchronous reset, because it is only evaluated on the clock front (synchronous with the clock). There are also cases where the reset is asynchronous, and then the active reset queue must appear in the block's list of sensitivities '''always'''.