To Use Devices (Resources) In Multitasking (Mutual Exclusive Control Of Resources) - Mitsubishi QD51 Programming Manual

8 MULTITASK PROCESSING

8.3 To Use Devices (Resources) in Multitasking (Mutual Exclusive Control of Resources)

System program
ZRESERVE 1
BASIC BASIC
program (A) program (B)
ZRESERVE 1
Two programs request
to use the printer.
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Resources refer to all of the hardware and software that can be used by the programs.
For example, they could be screens, printers, files, disks, optional boards, memory,
etc. When these devices are used in multiple programs being executed, some of them
can be grouped into one resource, or split into pieces to treat each of the pieces as a
single resource.
Example
Text screen
To split one resource into pieces and treat each of the pieces as a single resource
(Extension relays of the communication module EM0 through EM1023)
EM0 EM199
• • • • • • •
Mutual exclusive control of a resource means limiting access to that certain resource.
While one program is using a certain resource, other programs are prevented from
using the resource when multiple programs are executed simultaneously. This section
explains how to limit access to the specified resource to one program at a time while
multiple programs are being executed.
• Example of exclusive control of a printer
BASIC
program (A)
The program that made the request
first gets to use the printer.
The program that made the request
later has to wait.
+
EM200 EM299 EM300
• •
System program
ZRESERVE 1
Please wait
BASIC
program (B)
MELSEC-Q
Keyboard
EM1023
• • • • • • • • • • •
System program
ZRESERVE 1
BASIC
program (B)
After the program that made the request
first finishes using the printer,
the program that made the request
later gets to use the printer.
Thank you
BASIC
program (A)
Here you go
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