Section 1
SUPERVISOR PROTOCOL
7
TIME SLICING OF THE RS-485 SERIAL CHANNEL
When the sequencing mode is set to HOURS or COM ID# the machines will broadcast their
status (net status message) about once a second. To keep machines from sending mes-
sages simultaneously, time is sliced into periods (up to 9 maximum), one for each machine
and one for a monitor. A machine will only send a net status messages during it’s time slice
(see table below).
Time Slot COM ID# Time out
0 Monitor .5 sec
1 1 .125 sec
2 2 .125 sec
3 3 .125 sec
4 4 .125 sec
5 5 .125 sec
6 6 .125 sec
7 7 .125 sec
8 8 .125 sec
The number of time slots is determined by the LAST COM parameter. If the LAST COM
parameter is set to 4 then there will be 5 time slots (0 through 4). One for each machine and
one for the monitor.
The time slot for a monitor is longer because it may not be able to respond as quickly to a
message as the Supervisors.
The Supervisors establish what the current time slot is by either receiving messages or tim-
ing out. Any net status message establishes the time slot because the senders COM ID# is
imbedded in the message. For example if a net message from machine 2 is received then
time slot 2 has just finished and 3 is started.
If there is no message for a time out period (see table above) then it is assumed that the
machine assigned to that time slot is off line and the next time slot starts.
A machine sends a net status message immediately after a message is received from the
next previous machine, or that machines time slot has expired. For example if the time slot
has been established as 2 and either machine 2 sends a net status message or no mes-
sage is sent within .125 seconds, then machine 3 will send a net status message (if on line).
During time slot 0 a monitor may send a message, typically a status request or parameter
change message. A message that is sent by the monitor may need a response from one of
the machines. This response must come before the time out period (.5 sec).
Consider the following system with 4 machines with no monitor and machine 3 is off line.
Time Slot COM ID# Status Action
0 Monitor Off line .5 sec time out
1 1 On line Machine 1 net message
2 2 On line Machine 2 net message
3 3 Off line .125 sec time out
4 4 On line Machine 4 net message
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