Rockwell Automation 1772-LS_LSP,D17726.8.6 PROG/OPER MANUAL-MINI PLC-2/05 - Manual (Page 176)

Selectable Timed Interrupt
Chapter 15
15Ć2
Figure 15.1
Memory Organization
Selectable
Timed
Interrupt
Subroutine
Data
Table
User
Program
Other
Program
Subroutine
Subroutine Area
G LBL
010
00
XX YYY
XXX
010
00
RET
The Get instruction serves as a time base (xxx) for the STI. The Get instruction
can have any data table address (yyy) except a processor work area. It must be
used solely to designate the time base of the STI. The available time bases are:
1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, and 50 milliseconds. Your program, through the
use of a Get/Put instruction (see chapter 9) can change the time base of the
selectable timed interrupt. The subroutine must end with an unconditional
return instruction.
The Label instruction is optional and is only used when the main program wants
to call the subroutine based on other conditions rather than selected time
periods. If the subroutine timed interrupt is used as a direct subroutine with a
Label instruction, you can have seven subroutines plus the STI. If the
subroutine is not used as a direct subroutine, you can have eight subroutines
plus the STI.
Service time (Figure 15.2b) is factory set at approximately 2/3 of the timed
interrupt period. Subroutine execution time plus program transition time
(Figure 15.2c) should not exceed the maximum allowable service time (Figure
15.2b). When the program transition time plus subroutine execution time does
not exceed service time, there is sufficient time for the processor to scan
the subroutine.
Operational Overview