diff --git a/Urumbot/Urumbot-serial-servo.py b/Urumbot/Urumbot-serial-servo.py
index dbefe1ac564ea220d194ba02cb148fb874d624fd..9e605f782595ab6c550eeb7b660350b7c06b517c 100644
--- a/Urumbot/Urumbot-serial-servo.py
+++ b/Urumbot/Urumbot-serial-servo.py
@@ -28,13 +28,13 @@ xmin = ymin = 0
 count0 = count1 = countz = 0
 probstep0 = probstep1 = 0
 port0 = port1 = portz = 0
-time = stepus = 0
+t = stepus = 0
 pwmtime = 20000 # 50 Hz
 #
 # open ports and start alarm
 #
 def Connect():
-   global port0,port1,portz,time,countz,stepus
+   global port0,port1,portz,t,countz,stepus
    #
    try:
       port0 = serial.Serial(Port0Var.get(),baudrate=int(BaudRateVar.get()),timeout=0) # non-blocking
@@ -56,7 +56,7 @@ def Connect():
       print('can not open '+PortZVar.get())
    #
    try:
-      time = 0
+      t = 0
       stepus = int(float(StepTimeVar.get())*1000000)
       countz = int(PWMVar.get())
       signal.signal(signal.SIGALRM,AlarmHandler)
@@ -68,8 +68,8 @@ def Connect():
 # alarm handler
 #
 def AlarmHandler(signum,stack):
-   global count0,count1,time
-   time += stepus
+   global count0,count1,t
+   t += stepus
    #
    if ((port0 != 0) and (count0 != 0) and (probstep0 != 0)):
          if (random.random() <= probstep0):
@@ -90,9 +90,9 @@ def AlarmHandler(signum,stack):
                count1 += 1
    #
    if ((portz != 0) and (countz != 0)):
-      if (time < pwmtime):
+      if (t < pwmtime):
          return
-      time = 0
+      t = 0
       portz.write(countz.to_bytes(2,byteorder='little'))
 #
 # UI routines
@@ -174,15 +174,15 @@ def JogAngle():
    MoveCount()
 #
 def UpdateStepTime():
-   global time
+   global t
    signal.setitimer(signal.ITIMER_REAL,0,0)
-   time = 0
+   t = 0
    signal.signal(signal.SIGALRM,AlarmHandler)
    signal.setitimer(signal.ITIMER_REAL,float(StepTimeVar.get()),float(StepTimeVar.get()))
 #
 def UpdatePWM():
-   global time,stepus,countz
-   time = 0
+   global t,stepus,countz
+   t = 0
    stepus = int(float(StepTimeVar.get())*1000000)
    countz = int(PWMVar.get())
 #
@@ -417,4 +417,8 @@ Plot.grid(column=1,row=row,columnspan=4,padx=pad,pady=pad,sticky='sw')
 #
 # start mainloop
 #
-root.mainloop()
+#root.mainloop()
+while (True):
+   time.sleep(0.01)
+   update_idletasks()
+   update()