555taimerpa ver que pedo

The circuit is a 555 timer configured as a monostable multivibrator with an RC power-on reset. Originally I wanted approximately 1 ms monostable period, I scaled it down by 10 (Ct changed from 0.1 µF to 0.01 µF) so that the simulation can be viewed faster. An RC power-on reset is added to the basic monostable multivibrator circuit, my intention is to keep the output initially low until the trigger pulse after the 555 comes out of reset arrives. Unfortunately what is happening is that when the 555 comes out of reset the output immediately goes high even when trigger is inactive. This results to having a leading pulse that is spaced unevenly with the others and if this leading pulse terminates while the input signal is low (trigger active) it causes high frequency oscillation until trigger is deasserted. The presence and absence of this high frequency oscillation can be observed by adjusting the time constant of the POR (letting the leading output pulse terminate with trigger active/inactive). I studied the transistor level schematic diagram of the 555. My understanding is that when the 555 timer is powered on with RESET, TRIGGER, and THRESHOLD inactive, it's hard to predict the initial output state. On the other hand, at power-on and anytime, if RESET is asserted the output is forced low. Subsequently, when RESET is deasserted with TRIGGER and THRESHOLD inactive the output should stay low because the previous state is latched by regenerative action through the 4.7 kΩ feedback resistor. The 7/7.5 kΩ pull-up resistor cannot flip or unlatch this low output state. The output can only be switched high by asserting TRIGGER.