General Description: When sending an integer as the argument to the CONV_STD_LOGIC_VECTOR function found in the STD_LOGIC_ARITH package, Express assumes that the resulting STD_LOGIC_VECTOR will always be a signed number. In the follow example, the number 20 will be converted to 010100, not just 10100, and since a five bit signed vector has a range from 15 to -16, Express does not allow 20 as an input when the second input to the function is 5.
Error: Constant value 20 overflowed 'sized_int:range -16 to 15' in routine SYN_INTEGER_TO_SIGNED called from DELAY_COUNT20 line 37 in file 'convtest.vhd' (HDL-71)
Solution
Use a temporary vector that is one bit larger than the final vector. Assign the conversion to this vector, then assign all but the MSB to the final vector.
SIGNAL SYNC_DELAY : STD_LOGIC_VECTOR(4 downto 0); SIGNAL temp : STD_LOGIC_VECTOR(5 downto 0); CONSTANT DELAY : INTEGER := 20; ... temp <= CONV_STD_LOGIC_VECTOR(DELAY,6); --don't forget to increment the size by 1 SYNC_DELAY <= temp(4 downto 0);
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AR# 4644
Date
08/11/2003
Status
Archive
Type
General Article
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