UPGRADE YOUR BROWSER

We have detected your current browser version is not the latest one. Xilinx.com uses the latest web technologies to bring you the best online experience possible. Please upgrade to a Xilinx.com supported browser:Chrome, Firefox, Internet Explorer 11, Safari. Thank you!

AR# 16526

8.2i Schematic - How do I use constants in an ISE 8.2i schematic design?

Description

Keywords: ECS, constant, GND, ground, VCC, bus

In ECS, how do I place a constant value as a bus input to a schematic symbol?

This Answer Record is for ISE 8.2i and earlier. In ISE 9.1i, a Constant symbol has been added to the schematic editor for adding constant values to a bus.

Solution

ISE Schematic Editor does not currently have a constant value parameter that can be placed on a bus input to a schematic symbol. However, there are two simple ways to work around this problem, as described below:

1. You can name a bus input to apply VCC and GND to each bit as needed, as described in the following example:

a. Connect a net named "one" to a VCC symbol and a net named "zero" to a GND symbol.
b. Name an eight-bit bus "one,one,zero,zero,zero,one,one,zero" to give the bus a constant value of C6 (11000110).
NOTE: Be sure not to leave spaces between a comma and the next element of the compound bus name.

2. Generate your own constant schematic symbol using HDL code, as shown in the following example:

entity constant_symbol is
Port ( constant_out : out std_logic_vector(7 downto 0));
end constant_symbol;

architecture Behavioral of constant_symbol is

begin
constant_out <= "11110000";

end Behavioral;
AR# 16526
Date Created 09/03/2007
Last Updated 04/13/2009
Status Archive
Type General Article