at addresses 1 and 2. The 1 stands for a switch, DigiLink or
photocell.
The Err:0 is the error count. If the clock cannot see a board
for a moment it increments the error counter. This should
be zero. If it counts there is a problem with the bus. If a
switch is missing or a board is missing then there is proba-
bly a problem with that board or switch. (Or it is not plugged
in.)
(Also see next step before troubleshooting.)
6) Exit out of the BUS SCAN DISPLAY and tab down to
ERROR STATISTICS.
Tab down to clear and press ENTER. Then watch the dis-
play for a couple of minutes. If the error count starts rising
then highlight the address line as shown and scroll up the
address numbers to see which address is giving the errors.
If you know there are only addresses up to 10 on the bus
do not bother with addresses above.
A switch with a high error count may have an additional ter-
minator on it or should be replaced. It may work but eventu-
ally the problem that is causing errors will get worse and the
switch will not function. An error count of 0 in one minute is
what we are looking for. Systems can function however with
the error count just rising away. The reason is that the error
count is the number of times the clock tries to communicate
to a board and does not get through. It tries thirty or more
times if it does not receive an acknowledgment. If data is
corrupted due to noise then the receiving switch or board
will ignore it. The clock will then retry. This usually results in
almost any system having some sort of error count over a
period of time. Almost any system will have at least a few
errors in 1 hour.
A high error count with good cards means that the
bus has been run too close to high voltage wires
.
A switch on a long bus with an error count may have a ter-
minator on it that should not be there. It may also have too
low a dc voltage and need some additional power wire to
prevent voltage drop.
Page 61
ERROR STATISTICS:
OVERALL: 12340
ADR1
: 0
CMD1 : 0
CLEAR
3303000000 1110000000
0000000000 0000000000
0000000000 0000000000
0000000000 0000000000
0000000000 0000000000
0000000000 0000000000
0000000
Err:0
67