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Design Units
library clause use clause entity architecture port declaration generic declaration configuration package package body context clause
Types & Objects
std_logic std_logic_vector unsigned signed integer boolean signal variable constant array type
Concurrent Logic
concurrent assignment conditional signal assignment selected signal assignment with select component instantiation entity instantiation generate for generate if block statement alias
Processes
process sensitivity list process all rising_edge falling_edge clocked process combinational process variable in process wait statement wait until delta cycle
Sequential Statements
if elsif case statement for loop while loop next exit null statement assert report return
Numeric Logic
numeric_std conversion to_unsigned to_signed resize addition unsigned subtraction signed shift_left shift_right concatenation slice
FSM & RTL
state enum next-state logic Moore output Mealy output reset synchronous reset asynchronous clock enable counter shift register register file
Verification
testbench entity stimulus process clock generator assert equality severity levels textio write file input procedure in testbench generic testbench simulation stop
VHDL / FSM & RTL

clock enable

Learn clock enable in VHDL through a focused explanation, a dedicated construct-specific example, an engineering boundary, and a mastery check.

10 min read • Advanced

clock enable is an atomic VHDL topic inside FSM & RTL. This lesson focuses on how the clock enable construct is written, what it changes, and when it is the right tool.

Trace the example line by line. Identify the exact syntax for clock enable, the input state before it runs, and the resulting value, control flow, database state, hardware behavior, or runtime effect afterward. Neighboring lessons use different constructs rather than renamed copies of this one.

Topic-specific example

vhdl-07-07-clock-enable.vhd
vhdl Try It Live 
process(clk) begin if rising_edge(clk) then if en='1' then q<=d; end if; end if; end process;
Edge case / engineering note

For clock enable, test the boundary that belongs to this exact feature rather than a generic failure case. Check invalid or empty input, NULL/unknown state, numeric limits, transaction or exception behavior, synthesis/runtime constraints, ownership/permission rules, or backtracking/control-flow effects where they apply.

Content source & attribution
Original Syntaxis Content · Original Syntaxis Content

Lesson quizzes

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