Programmable Frequency Divider
Posted on Sep 7, 2012 11421
This divider uses a variable-length shift register, a type-D flip-flop, and an inverter. The clock feeds the
flip-flop clock input and the output of the shift register feeds the D input of the flip-flop. The FF output is tied back to the reset input of the shift register so that each clock pulse shifts a " " into the 4557. N+1 cycles after the reset pulse is removed. The first "1" will propagate through the register output. The "1" is latched into the FF on the clock"s next falling edge and fed back to the 4557 reset pin, which resets the shift register to zero. When a zero is clocked into the flip-flop on the next falling clock edge, the reset is removed, restarting the process. The divide ratio is (N+2), where = the binary number that is programmed into 4557.