Denso RC5 Specifications download pdf (Page 68)

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2.3 Multitasking

A PAC language program can concurrently execute progress management of

multiple programs. Each program forms its own motion process and this is

called a task.

Concurrent progress management of multiple programs means that there are

multiple tasks present. This is called multitasking.

2.3.1 Priority

To run a task using the RUN command, designate a priority. As a result all

tasks have their own priority.

The VS series robot checks task priority at fixed time intervals during program

execution, and changes tasks so that the tasks in the waiting status with the

highest priority are executed.

As a result the program is executed in sequence of the highest priority. If tasks

have the same priority, the robot controls the tasks so that the task execution

order alternates at each fixed time interval. Since the alternating task

execution requires such a short time to be controlled it appears as if multiple

programs are executed concurrently.

2.3.2 Communication among Tasks

When the robot is controlled in multitasking operation, tasks sometimes need

to be synchronized or exclusively controlled so those tasks do not operate at

the same time. In any case, communication among tasks is required since the

tasks must exchange signals.

For communication among tasks semaphores are generally used but I/O can

also be used with the VS series robots.

2.3.2.1 Semaphore

Up to 32 semaphores can be created as required. Prior to using semaphores,

if a semaphore is created using a CREATESEM command the semaphore ID

can be obtained. This semaphore ID can be used to designate a specific

semaphore.

In either synchronization control or exclusive control, a task waiting for a

command from another task will execute a TAKESEM command and then wait

for the task to send a command to execute using a GIVESEM command. If the

task sending a command is ready, it executes a GIVESEM command and

allows the task, which is waiting for a semaphore, to execute the process.

One GIVESEM command is valid only for a task that is waiting for one

semaphore.

When multiple tasks are waiting for a semaphore with the same semaphore ID,

one of two queuing (execution waiting) systems can be selected for processing

(first-come order or priority order starting from a specific task). Use the

CREATESEM command to designate the queuing system.

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Denso RC5 Specifications Page 68

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