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<@U01TK0ML9H9> you can use 2 or more generators each generating a finite number of pulses:

<@U01TK0ML9H9>... or you can use a B-source to enter an arbitrary waveform. Below example generates a varying frequency square wave.

<@U01819B63HP> Thanks for sharing this setup. It should suffice my requirement.

<@U01819B63HP> I have observed that during `TRAN` simulation the ouput `.raw` file data does not get overwritten everytime I run transient simulation but the data for new simulation get appended to last simulation and that reflects in the waveform.

How to ensure that for every new TRAN simulation run the output `.raw` gets overwritten and not appended ?

<@U01TK0ML9H9> you must not have `set appendwrite` before `write` in your spice commands.

Is appendwrite required befor both `OP` and `TRAN` ?

if you put `set appendwrite` after the OP `write` it will create a new raw file, then tran `write` will append data.

Can you please suggest what will be the correct way of running both `OP` and T`RAN` and save their data in same `.raw` file for below code .


`.control`
`reset`
`op`
`write pfd_cp.raw`
`set appendwrite`

`tran 0.1n 6u uic`
`step param R1 R1_start R1_stop R1_step`
`remzerovec`
`write pfd_cp.raw`
`set appendwrite`

`.endc`

The code above is correct. I don't know the function of the `step` line, so remove that line, the reset line also has no function here.
The sequence:
`op`
`write pfd_cp.raw`
`set appendwrite` 
`tran ...`
`remzerovec`
`write pfd_cp.raw`
is correct. If it does not create a new raw file then file the bug to ngspice developers.