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VHDL Tutorial |
Time type in VHDL | ||
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. Time
VHDL has a predefined type called time that is used to represent simulation times and delays. We can write a time value as a numeric literal followed by a time unit. For example:
5 ns 22 us 471.3 msec
Notice that we must include a space before the unit name. The valid unit names are
fs ps ns us ms sec min hr
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Contact : webmaster@freehost7com The type time includes both positive and negative values. VHDL also has a rede- fined subtype of time, delay_length, that only includes non-negative values. Many of the arithmetic operators can be applied to time values, but with some restrictions. The addition, subtraction, identity and negation operators can be applied to yield results of type time. A time value can be multiplied or divided by an integer or real value to yield a time value, and two time values can be divided to yield an in- teger. For example:
18 ns / 2.0 = 9 ns, 33 ns / 22 ps = 1500
Finally, the abs operator may be applied to a time value, for example:
abs 2 ps = 2 ps, abs (–2 ps) = 2 ps
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