AR# 16526: 8.2i Schematic - How do I use constants in an ISE 8.2i schematic design?
8.2i Schematic - How do I use constants in an ISE 8.2i schematic design?
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.
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;