Assic 15th Lecture
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The document discusses timescale directives in Verilog HDL. It explains that timescale directives allow modules to specify different time units, like 100 ns and 1 μs. The `timescale directive sets the reference time unit and time precision for a module. It has the format `timescale <reference_time_unit> / <time_precision>, where only 1, 10, and 100 are valid for time unit and precision. An example shows two identical modules with different time units, causing statements in one module to execute ten times more frequently than the other.
Assic 15th Lecture
- 1. 1 Verilog HDLVerilog HDL ASIC DESIGN USING FPGA BEIT VII KICSIT October 2 2012 Lecture 15
- 2. 2 Time Scales October 2 2012 • Delay values in one module need to be defined by using certain time unit, e.g., 1 µs, • Delay values in another module need to be defined by using a different time unit, e.g. 100 ns. •Verilog HDL allows the reference time unit for modules to be specified with the `timescale compiler directive. `timescale <reference_time_unit> / <time_precision> Lecture 15
- 3. 3 Time Scales October 2 2012 • The <reference_time_unit> specifies the unit of measurement for times and delays. • The <time_precision> specifies the precision to which the delays are rounded off during simulation. • Only 1, 10, and 100 are valid integers for specifying time unit and time precision. Lecture 15
- 4. 4 Time Scales October 2 2012 • Example Lecture 15
- 5. 5 Time Scales October 2 2012 • Example Lecture 15
- 6. 6 Time Scales October 2 2012 • The two modules dummy1 and dummy2 are identical in all respects, except that the time unit for dummy1 is 100 ns and the time unit for dummy2 is 1 µs. • Thus the $display statement in dummy1 will be executed 10 times for each $display executed in dummy2. Lecture 15
- 7. 7 Time Scales October 2 2012 • The $time task reports the simulation time in terms of the reference time unit for the module in which it is invoked. • The first few $display statements are shown in the simulation output below to illustrate the effect of the `timescale directive. • Notice that the $display statement in dummy2 executes once for every ten $display statements in dummy1. Lecture 15
- 8. 8 Time Scales October 2 2012 Lecture 15