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Comprehensive Guide to VHDL Counters: Ripple and Synchronous Designs

Explore the fundamentals of VHDL counters with this guide, detailing Ripple and Synchronous counters. Understand the operation of 4-bit binary counters, including the use of flip-flops for counting and how to implement them in VHDL. This resource covers aspects such as counting mechanics, loading data, and reset functions. Through clear examples and timing diagrams, learn how to design and simulate various counter circuits, ensuring synchronization with clock inputs. Perfect for beginners to advanced users in FPGA and digital design!

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Comprehensive Guide to VHDL Counters: Ripple and Synchronous Designs

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  1. VHDL Counters CSET 4650 Field Programmable Logic Devices Dan Solarek

  2. E E E E E Reset E E E E E E E E Counters • Any sequential circuit whose state diagram is a single cycle.

  3. Ripple Counters • Uses trigger or “T” flip-flops • Each flip-flop acts as a “divide-by-two” with respect to the CLK input • Count ripples through the flip-flops

  4. Ripple Counter Timing

  5. LSB Serial enable logic MSB Synchronous Counters • Synchronizing the flip-flops with the clock assures that all change together

  6. LSB Parallel enable logic MSB Synchronous Counter • A parallel version of the synchronous counter

  7. 74x163 MSI 4-Bit Counter

  8. 74x163 Internal Logic Diagram • XOR gates embody the “T” function • Mux-like structure for loading

  9. Counter Operation • Free-running 16 • Count if ENP andENT both asserted. • Load if LD is asserted(overrides counting). • Clear if CLR is asserted (overrides loading and counting). • All operations take place on rising CLK edge. • RCO is asserted if ENT is asserted and Count = 15. Lect #12 Rissacher EE365

  10. Free-Running 4-bit ’163 Counter • Timing diagram for a “divide-by-16” counter Lect #12 Rissacher EE365

  11. 4-Bit Binary Counter • VHDL for a 4-bit binary counter • Behavioral architecture library ieee; -- A four-bit counter. use ieee.std logic 1164.all; use ieee.std logic unsigned.all; entity count4 is port(Resetn, E, clk : in STD_LOGIC; Q : out STD_LOGIC_VECTOR (3 downto 0)); end count4; architecture Behavior of count4 is signal Count : STD_LOGIC_VECTOR (3 downto 0); begin process (clk, Resetn) begin if Resetn = '0' then Count <= "0000"; elsif (clk'EVENT and clk = '1') then if E = '1' then Count <= Count + 1; end if; end if; end process; Q <= Count; end Behavior;

  12. 4-Bit Binary Counter • VHDL for a 4-bit binary counter • Behavioral architecture library IEEE; use IEEE.std_logic_1164.all; use IEEE.std_logic_arith.all; --to get arithmetic operations entity counter4 is port( CLK, CLR_L: in STD_LOGIC; Q: out UNSIGNED(3 downto 0); end counter4; architecture counter4_arch of counter4 is signal IQ: UNSIGNED (3 downto 0); --Internal counter state begin process ( CLK, IQ ) begin if (CLK'event and CLK='1') then -- Rising edge of clock if CLR_L='0' then IQ <= (others => '0'); --Synchronous Reset else IQ <= IQ + 1; --Increment count end if; end if; Q <= IQ; -- Output end process; end counter4_arch;

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