1
CSM_PLC Basic_TG_E_1_1
Technical Guide for PLC Basic
Introduction
This guide will describe the terminology needed for basic operation of the SYSMAC PLC (Programmable Controller), for clients new to our PLCs.
This guide does not cover technical details regarding the setting of the FA System or PLC programming after purchase.
I/O Refresh
With the PLC (Programmable Controller), commands from user programs designed by the client are executed one by one and processed by
reading and writing information in the internal PLC memory area (At OMRON, we call this the "I/O Memory").
At the same time, packages of data from sensors/switches that are directly connected to the basic I/O unit are exchanged with data in the PLC
internal I/O Memory, at specific times. This process to totally exchange external data and internal I/O memory data is called "I/O Refresh
Operation".
It is important to know the timing by which the I/O Refresh will be executed when considering the operation of the FA System and User Programs
designed by the client. In the case of the SYSMAC PLC, this I/O Refresh operation is performed immediately following the execution of all other
commands. (See Figure below)
Cycle Time
In terms of the PLC processing cycle, the cycle time is the time from the execution (commencement) of the I/O Refresh operation to the execution
(processing) of the following I/O Refresh.
The cycle time includes time for overhead processing (self-diagnosis), execution of user programs, I/O Refresh processing and the processing of
peripheral services.
• When the cycle time is long, the cycle for updating data from outside of the PLC and the I/O response time are also longer, making it impossible
to implement changes that are input at a rate faster than the cycle time.
• When the cycle time is short, I/O response time is also shortened, which allows high speed processing.
• As the cycle time changes, the command execution cycle and I/O response times also change.
In the case of the SYSMAC PLC, the cycle time can be requested in the following manner:
Cycle Time = Overhead Processing Time + Total Command Execution Time + I/O Refresh Time + Peripheral Service Time
The calculation methods for each execution time for the SYSMAC PLC are included in the product manual.
Common Proce
ss
ing
(
S
elf-Di
a
gno
s
i
s
)
Re
a
d/Write
P
a
ck
a
ge
Exch
a
nge
Exec
u
te Progr
a
m
I/O Memory
Ch
a
nge (
a
fter
a
ll
comm
a
nd
s
exec
u
ted)
Peripher
a
l
S
ervicing
PLC
Proce
ss
ing Cycle
PLC
In
s
ide PLC (CPU Unit)
B
as
ic I/O Unit
or
bu
ilt-in I/O
Refre
s
h with extern
a
l device
s
Extern
a
l D
a
t
a
(
S
en
s
or,
S
witch, Act
ua
tor etc.)
I/O Refre
s
h
0 0 1 1 1 0 1 0
1 1 0 1 1 0 0 0
1 0 1 0 1 0 0 1
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
1 0 1 1 1 0 1 1
1 1 0 0 1 0 1 0
1 0 0 0 1 1 0 1
0 1 0 1 0 1 0 0
0 1 1 0 1 0 1 0
