Simulate serial RS232 data to use as a PWL file for LTspice

pwl_serstream.py

#!/usr/bin/python

data = "asdfg"
bps = 115200
num_databits=8
parity = 'n'
num_stopbits = 1

lvl_0 = 3.3
lvl_1 = 0.0

if type(data) is str:
    data = [data]

out = oldout = 0
time = 0.0
timestep = 1.0/bps
risetime = falltime = timestep / 20.0
idletime = timestep * (num_databits + 3)

def do_timestep(output, step):
    global time
    global out, oldout
    global lvl_0, lvl_1

    out = output
    time_diff = 0

    if oldout!= out:
        if oldout > out:
            # fall
            time_diff = falltime
        else:
            # rise
            time_diff = risetime
        lvl = (lvl_0 if oldout == 0 else lvl_1)
        print ("{0:g} {1:g}".format(time, lvl))
        lvl = (lvl_0 if out == 0 else lvl_1)
        print ("{0:g} {1:g}".format((time + time_diff), lvl))

        oldout = out

    time += step
    return time

do_timestep(0,0)

# idle
do_timestep(0, idletime)

for sentence in data:
    # start bit
    out = 1
    do_timestep(out, timestep)

    for char in sentence:
        # print("# {}").format(char); 
        par = 0

        for bit in range(0, num_databits):
            out = (ord(char) >> bit) & 1
            par = bool(parity) ^ bool(out)

            do_timestep(out, timestep)
            
        if parity == 'e':
            # even parity
            out = par
        elif parity == 'o':
            # odd parity
            out = ~par
        do_timestep(out, timestep)

        # stop bits
        out = 0
        do_timestep(out, (timestep * num_stopbits))

    # idle
    out = 0
    do_timestep(out, idletime)

Your code has bugs in it.
Line 37: print ("{0:g} {1:g}".format(time, lvl));
Line 39: print ("{0:g} {1:g}".format((time + time_diff), lvl));

The brackets are wrong.
Also, in Python, the lines do not need ";" on the end :)

thx for this suggestion

Script was otherwise very useful, thanks!

I notice that the baudrate is off by a factor of 2 when I use this in Ltspice, so at line 17, I changed to timestep = 1.0/bps/2