How does Verilog register with enable signal, problem of understanding simulation results?
In this case, the clk, enable and d signals all changed at the same instant in the testbench, so by the time the Nbit_register module was evaluated, it “saw” the rising edge of clk with enable = 1 and d = 0xFFFFFFFF, so that is what it captured.
When does the Por signal reset the shift register?
The external POR signal sets the 3 flip-flops of the shift register asynchronous to ‘0’ (= reset). Since it is asynchronous to the system clock, it is called reset_a and is active low. After the POR signal has been deactivated, its inactive value ‘1’ is clocked into the shift register as soon as the system clock is present.
Can a register change at the same time as the active clock?
In general, you should avoid having the inputs to any register change at the same instant as the active clock edge. In physical circuits, this could lead to metastability issues, and simulators give results that are confusing at best.
What is a power-on reset for an FPGA?
A power-on reset for an FPGA is implemented in Verilog and VHDL languages. What is a Power-on Reset? If a synchronous reset is executed at system startup, it is possible that there is no clock signal at this time, since the clock source itself may be subject to a reset. Therefore, the synchronous reset can be ineffective.
How to enable or disable signal logging for a model?
To log a signal, mark it for logging. For details, see Configure a Signal for Logging. Enable or disable logging globally for all signals that you mark for logging in a model. By default, signal logging is enabled. Simulink ® logs signals if the Configuration Parameters > Data Import/Export > Signal logging parameter is checked.
When do I need to use signal logging in Simulink?
Simulink ® logs signals if the Configuration Parameters > Data Import/Export > Signal logging parameter is checked. If the option is not checked, Simulink ignores the signal logging settings for individual signals. When signals are marked for logging, the signal data logs to the workspace and to the Simulation Data Inspector.
Is the register with enable signal active at 5NS?
At 5ns the enable signal is not active so the rising edge of the clock samples this signal as disabled. If you want to sample enable as high at t=25 ns you have to set it at 15ns and it must remain set at least until t=25ns.