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Re: i want to create 100hz and pw 1ms in 555 timer
Each cycle of 100Hz has a duration of 1/100= 0.01 seconds. You want each pulse to be 0.001 seconds long so the longer pulse must be 0.01 - 0.001= 0.009 seconds (9ms) long.
The datasheet for a 555 tells you that its timing capacitor charges slowly (the 9ms time) through two series resistors but discharges quickly (the 1ms time) through only one of the two resistors.
The datasheet shows a formula for the resistor and capacitor and limits for their values then you use a little simple arithmetic to calculate them.