See Also

Parameterized counter megafunction. The lpm_counter megafunction is a binary counter that features an up, down, or up/down counter with optional synchronous or asynchronous clear, set, and load ports.

Altera^® recommends using the lpm_counter function instead of any other type of binary counter.

This topic contains the following information:

• AHDL Function Prototype (also applies to Verilog HDL)
• VHDL Component Declaration
• VHDL LIBRARY-USE Declaration (not required if the VHDL Component Declaration is used)
• Port Descriptions
• Parameter Descriptions
• Truth Table/Functionality
• Typical Implementation
• Resource Usage

FUNCTION lpm_counter (data[LPM_WIDTH-1..0], clock, clk_en, cnt_en, updown, cin,
      aclr, aset, aconst, aload, sclr, sset, sconst, sload)
   WITH (LPM_WIDTH, LPM_DIRECTION, LPM_MODULUS, LPM_AVALUE, LPM_SVALUE, CARRY_CNT_EN, LABWIDE_SCLR)
   RETURNS (q[LPM_WIDTH-1..0], eq[15..0] );

COMPONENT lpm_counter
   GENERIC (LPM_WIDTH: POSITIVE;
      LPM_MODULUS: NATURAL := 0;
      LPM_DIRECTION: STRING := "UNUSED";
      LPM_AVALUE: STRING := "UNUSED";
      LPM_SVALUE: STRING := "UNUSED";
      LPM_PVALUE: STRING := "UNUSED";	  
      LPM_TYPE: STRING := "LPM_COUNTER";
      LPM_HINT : STRING := "UNUSED");
   PORT (data: IN STD_LOGIC_VECTOR(LPM_WIDTH-1 DOWNTO 0) := (OTHERS => '0');
      clock: IN STD_LOGIC;
      clk_en, cnt_en, updown: IN STD_LOGIC := '1';
      sload, sset, sclr, aload, aset, aclr, cin: IN STD_LOGIC := '0';
      cout: OUT STD_LOGIC;
      --eq: OUT STD_LOGIC_VECTOR (15 DOWNTO 0);	  
      q: OUT STD_LOGIC_VECTOR(LPM_WIDTH-1 DOWNTO 0));
END COMPONENT;

Implementation of the lpm_counter function does not include the LPM_PVALUE parameter.

LIBRARY lpm;
USE lpm.lpm_components.all;

INPUT PORTS

OUTPUT PORTS

Inputs										Outputs	Function
aclr	aset	aload	clk_en	clock	sclr	sset	sload	cnt_en	updown	q[LPM_WIDTH-1..0]
1	x	x	x	x	x	x	x	x	x	000...
0	1	x	x	x	x	x	x	x	x	111...
0	1	x	x	x	x	x	x	x	x	LPM_AVALUE	Asynchronous set to value specified for LPM_AVALUE
0	0	1	x	x	x	x	x	x	x	data[]	Asynchronous load from data[] input
0	0	0	0	x	x	x	x	x	x	q[]	Hold current count value
0	0	0	1		1	x	x	x	x	000...	Synchronous clear
0	0	0	1		0	1	x	x	x	111...	Synchronous set
0	0	0	1		0	1	x	x	x	LPM_SVALUE	Synchronous set to value specified for LPM_SVALUE
0	0	0	1		0	0	0	0	0	q[]	Hold current count value
0	0	0	1		0	0	1	x	x	data[]	Synchronous load from data[] input
0	0	0	1		0	0	0	1	1	q[]+1	Count up
0	0	0	1		0	0	0	1	0	q[]-1	Count down

The lpm_counter function offers four different modes that allow you to force the count value to a specific number. You can use each of the modes either synchronously (port names starting with an "s") or asynchronously (port names starting with an "a"). You can also combine the modes.

The following table summarizes the resource usage for an lpm_counter function used to implement a 16-bit counter with an up/down control, a count enable input, a synchronous load input, and an asynchronous clear input. Logic cell usage scales linearly in proportion to counter width.

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