ADLINK HSL-AI16AO2-M-VV/-AV - Manual (Page 29)

16 Introducing HSL
The teacher (master) sends the message “ID.#, what is your latest
input status” to all students (slave I/O modules). Every student
(with ID.#) then gives his answer. The teacher writes the answers
on the blackboard (RAM on master cards). When someone (user’s
AP) wants to know the students’ answers, he refers to the black-
board. All input information are saved in the memory.
These two procedures take turn and repeat on every slave mod-
ule. After each cycle, each slave module sets its newest output
status and the master gathers all these information from the mem-
ory. We simulate the polling communication cycle through a
teacher-student conversation:
Teacher: Student No. 1, your output vales are ##, what’s your lat-
est input status?
Student No. 1: My input status is ##
Teacher writes the answer on the blackboard.
Teacher: Student No. 2, your output vales are ##, what’s your lat-
est input status?
Student No. 2: My input status is ##
Teacher writes the answer on the blackboard.
Until…
Teacher: Student No. 63, your output vales are ##, what’s your lat-
est input status?
Student No. 63: My input status is ##
Teacher writes the answer on the blackboard.
The polling cycle is now complete. The process repeats from Stu-
dent No. 1.)