![]() ![]() ![]() ![]() The simulation of the VHDL code for the clock divider by power of two is reported in Figure6 Figure6 – Clock Divider by a power of two Simulation Remember that this VHDL code it is still synthesizable, so you can use it without any problem, but your clock divider start condition is unknown. The VHDL code for a clock divider by 2 is: signal clk34_66 : std_logic:='0' Sometimes this approach is used to generate a clock with 50% duty cycle even starting from a source clock that has a duty cycle different from 50%įigure4 show an example where the source clock has duty cycle 34/66 and the divided clock has a duty cycle of 50% Figure4 – Clock divider by two simulation example This is the simplest clock divider you can implement into an FPGA or ASIC. If the clock we need is simply the system clock divided by two, we can implement a simple divider using a flip-flop and inverter: Figure3 – Clock divider by two example Clock3 offset with respect to clock1 is 50 ns = 100 ns/2 (i.e.Clock2 offset with respect to clock1 is 25 ns = 100 ns/4 (i.e.Sometimes the PLL are used to modify the clock phase or to generate different clocks at the same frequency with different phase relationship. So you can generate internal FPGA clock as multiple or sub-multiple of the external system clock.įigure1 – FPGA with internal clock divider Many modern FPGAs have the possibility to generate internal clocks, different from the external clocks, using internal PLL hard macro. With system clock, I mean the clock that is coming from an external board oscillator. all entity Clock_Pulse_Timer is generic (įreq_div : integer : = 16 -how many input clocks before an output is triggered.Often, inside our FPGA design, we have the necessity to generate a local clock from the system clock. Ideal for use with a SIPO shift register or when precise, -ěy James E Logan, - VHDL 2008 library ieee use ieee. This implements a timed clock pulse generator. ![]()
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