                        The Time Constant

   The Time Constant (hereafter called TC) is a delay used after 
each keypress sent to the scanner. When a key is pressed on the 
scanner, it must be held down for a definite amount of time before 
the scanner gets around to checking it. The scanner will not normally 
recognize another keypress until the key has been released. So, the
key must be released and no other key pressed until the scanner has
had time to see that no keys are pressed. The main program sends the
commands to press a key to the Scanner Interface Unit. The key is held
closed and then open for the correct amount of time by the program 
within the Interface Unit. The main program must not send another key
press command until that time has passed. This is where the TC comes
into play. The TC is a delay within the main program that happens 
after every keypress command. If the keypresses are sent too fast, 
some will be missed resulting in errors at the scanner. 
   It is unlikely that you will overrun the scanner while controlling
it from the PC's keyboard (unless you have a super fast computer and
super fast fingers). However, during AutoPrograming of the scanner
this is quite possible. Each personality file has a default TC value
which is used if the TC entry in the setup is left blank. If a value
is entered for TC in the basic parameters setup then that value is 
used for the TC. This entry was provided for users who have slow 
computers. They can optimize their autoprograming rate by taking 
advantage of the slower processing time to provide the required 
delays. 
   How do you find an optimum TC? Prepare a short autoprogram file
(three or for channels to program). Enter the default Time Constant 
(PRO2004/5 = 105 , PRO2006 = 90) and then try to program the scanner
with the file. Watch your scanner's error indicator. If you see it
flash on then the TC needs to be increased. If you don't see the 
error indication, then check that the channels were programed 
correctly. If not, then increase the TC. If the scanner was programed
correctly, then decrease the TC and try again. Repeat the process 
until the scanner is programed correctly with the smallest possible 
TC, then add a little more for a safety margin. 
   What happens if you can't get the scanner to program correctly
regardless of the TC used? If you are using the 2006 personality file
you will have to switch to the 2004/5 personality file. There appears
to be some model differences among the 2006's with regards to internal
timing. We have not seen any problems with the 2004/5 models. 
   The value for the TC is in milliseconds. If you want to see the
effect of the Time Constant, enter 500. This will cause a half second
delay after every keypress and is very obvious when autoprograming.
Changes to the TC take effect immediately (ie; they don't have to be
saved and the program restarted) but don't forget to save the setup when
an optimum setting is found.




