AR# 2145

Description

General Description:

How do I instantiate a pull-up/pull-down using Synplify in HDL?

NOTES:

- For CPLD devices, pull-ups in the IOBs are not user-controllable during normal operation. These pull-up resistors are active only during device programming, power-up, and the erase cycle.

- For Virtex, please see (Xilinx Answer 948) for details pertaining to Synplify versions 5.1.4 and earlier.

- You can instantiate PULLUP/PULLDOWN cells by using the Xilinx family library supplied with Synplify. Please see (Xilinx Answer 244) for details of instantiating Xilinx-specific cells.

- Synplify 5.0.7 introduced two new attributes that can be used to implement pull-ups and pull-downs: xc_pullup and xc_pulldown.

Solution

VHDL

IOB Pull-up/Pull-down with a Registered Bidirectional I/O Using Instantiated Cells

library ieee, xc4000;

use ieee.std_logic_1164.all;

use xc4000.components.all; -- Include Synplify Xilinx Macro Library

entity BIDIR_EX1 is

port (SIGA, SIGB : inout std_logic;

INA, INB, EN, CLK : in std_logic);

end BIDIR_EX1;

architecture XILINX of BIDIR_EX1 is

component PULLUP

PORT ( O: out std_logic );

end component;

component PULLDOWN

PORT ( O: out std_logic );

end component;

signal INA_INT, OUTA_INT : std_logic;

signal INB_INT, OUTB_INT : std_logic;

begin

U0 : PULLUP port map (O => SIGA);

U1 : PULLDOWN port map (O => SIGB);

-- Registered Input path

process (CLK)

begin

if rising_edge(CLK) then

INA_INT <= SIGA;

INB_INT <= SIGB;

end if;

end process;

-- Registered Output path with tri-state

SIGA <= OUTA_INT when (EN = '0') else 'Z';

SIGB <= OUTB_INT when (EN = '0') else 'Z';

process (CLK)

begin

if rising_edge(CLK) then

OUTA_INT <= INA_INT and INA;

OUTB_INT <= INB_INT and INB;

end if;

end process;

Verilog

- A pull-up must be attached to a long-line.

- Internal pull-down connections are illegal.

- Pull-downs are only available on I/O pads.

// Include Synplify Xilinx Macro Libraries

`include "/products/synplify/lib/xilinx/xc4000.v"

module LONG_LINE_EX1 (INBUSA, EN, SIGA, OUT_SIG);

input [2:0] INBUSA, EN;

input [1:0] SIGA;

output OUT_SIG;

wire INT_SIG;

PULLUP U0 (.O (INT_SIG));

// Infer tri-state buffers

assign INT_SIG = (EN[0] == 1'b1) ? INBUSA[0] & SIGA[0] : 1'bz;

assign INT_SIG = (EN[1] == 1'b1) ? INBUSA[1] & SIGA[0] : 1'bz;

assign INT_SIG = (EN[2] == 1'b1) ? INBUSA[2] & SIGA[0] : 1'bz;

// glue logic

assign OUT_SIG = SIGA[1] ^ INT_SIG;

endmodule

VHDL

- A pull-up should be attached to a long-line.

- Internal pull-down connections are illegal.

- Pull-downs are only available on I/O pads.

library ieee, xc4000;

use ieee.std_logic_1164.all;

use xc4000.components.all; -- Include Synplify Xilinx Macro Libraries

entity LONG_LINE_EX1 is

port (INBUSA, EN : in std_logic_vector(2 downto 0);

SIGA : in std_logic_vector(1 downto 0);

OUT_SIG : out std_logic);

end LONG_LINE_EX1;

architecture XILINX of LONG_LINE_EX1 is

component PULLUP

PORT (O : out std_logic);

end component;

signal INT_SIG : std_logic;

begin

U0 : PULLUP port map (O => INT_SIG);

-- Infer tri-state buffers

INT_SIG <= INBUSA(0) and SIGA(0) when (EN(0) = '1') else 'Z';

INT_SIG <= INBUSA(1) and SIGA(0) when (EN(1) = '1') else 'Z';

INT_SIG <= INBUSA(2) and SIGA(0) when (EN(2) = '1') else 'Z';

-- glue logic

OUT_SIG <= SIGA(1) xor INT_SIG;

end XILINX;

Verilog

IOB Pull-up/Pull-down with a Registered Bidirectional I/O Using Instantiated Cells

// Include Synplify Xilinx Macro Libraries

`include "/products/synplify/lib/xilinx/xc4000.v"

module BIDIR_EX1 (SIGA, SIGB, INA, INB, EN, CLK);

inout SIGA, SIGB;

input INA, INB, EN, CLK;

reg INA_INT, OUTA_INT;

reg INB_INT, OUTB_INT;

PULLUP U0 (.O (SIGA));

PULLDOWN U1 (.O (SIGB));

// Registered Input path

always @(posedge CLK)

begin

INA_INT = SIGA;

INB_INT = SIGB;

end

// Registered Output path with tri-state

assign SIGA = !EN ? OUTA_INT : 1'bz;

assign SIGB = !EN ? OUTB_INT : 1'bz;

always @(posedge CLK)

begin

OUTA_INT = INA_INT & INA;

OUTB_INT = INB_INT & INB;

end

endmodule

VHDL

IOB Pull-up/Pull-down with a Registered Bidirectional I/O Using the "xc_pulldown"/"xc_pullup" Attributes

(This is available only for Synplify versions 5.0.7 and later.)

library ieee, synplify;

use ieee.std_logic_1164.all;

use synplify.attributes.all; -- Define Synplify attributes

entity BIDIR_EX1 is

port (SIGA, SIGB : inout std_logic;

INA, INB, EN, CLK : in std_logic);

attribute xc_pullup of SIGA : signal is true;

attribute xc_pulldown of SIGB : signal is true;

end BIDIR_EX1;

architecture XILINX of BIDIR_EX1 is

signal INA_INT, OUTA_INT : std_logic;

signal INB_INT, OUTB_INT : std_logic;

begin

-- Registered Input path

process (CLK)

begin

if rising_edge(CLK) then

INA_INT <= SIGA;

INB_INT <= SIGB;

end if;

end process;

-- Registered Output path with tri-state

SIGA <= OUTA_INT when (EN = '0') else 'Z';

SIGB <= OUTB_INT when (EN = '0') else 'Z';

process (CLK)

begin

if rising_edge(CLK) then

OUTA_INT <= INA_INT and INA;

OUTB_INT <= INB_INT and INB;

end if;

end process;

end XILINX;

Verilog

IOB Pull-up/Pull-down with a Registered Bidirectional I/O Using the "xc_pulldown"/"xc_pullup" Attributes

(This is available only for Synplify versions 5.0.7 and later.)

module BIDIR_EX2 (SIGA, SIGB, INA, INB, EN, CLK);

inout SIGA /* synthesis xc_pullup = 1 */;

inout SIGB /* synthesis xc_pulldown = 1 */;

input INA, INB, EN, CLK;

reg INA_INT, OUTA_INT;

reg INB_INT, OUTB_INT;

// Registered Input path

always @(posedge CLK)

begin

INA_INT = SIGA;

INB_INT = SIGB;

end

// Registered Output path with tri-state

assign SIGA = !EN ? OUTA_INT : 1'bz;

assign SIGB = !EN ? OUTB_INT : 1'bz;

always @(posedge CLK)

begin

OUTA_INT = INA_INT & INA;

OUTB_INT = INB_INT & INB;

end

endmodule