Introduction.

Workshop PG5
Project management
6.1 Sequential Blocks (SB 0 ... 31)
SB’s (Sequential Blocks) work different then the program blocks we learned about
previously. SB’s are very efficient if you have an application where you have to do
several things in a defined sequence.
Example Elevator: “close the door” => “wait until the door is closed” => “move the
elevator to the first floor” => “wait until the elevator has reached the first floor” =>
“open the door again”
Because we don’t know how long your program will wait on a particular event (
milliseconds, minutes, days?) before it can continue with the next STEP, you can’t
know the cycle time of an SB. Therefore it’s important to analyze your program and
separate sequential problems in your application from parts which absolutely have to
be in a cyclic block.
Example: If you have an emergency switch on your application, then you want to be
sure that this information is updated regularly. Therefore such information would
never be put into a SB but into a COB.
Typical Graftec Chart
SB sequence
starts here.
The SB number.
(each SB is assigned
a number)
SB sequence
ends here.
SB page
number.
PG5-06-E.doc © Saia-Burgess Controls Ltd. Page 6-1