Chapter 4 CPU Specifications
XBC E-Type Main Unit 4-7 Ver. 1
4.4.3 Scan time
The processing time from program step 0 to the next step 0 is called “Scan Time”.
1. Scan time is the sum of the processing time of scan program and interrupt program prepared by
the user and PLC internal time. It is distinguished by the following formula.
a. Scan time = Scan program processing time ＋ Interrupt program processing time ＋
PLC internal processing time
i. Scan program processing time = processing time of user program except
interrupt program
ii. Interrupt program processing time = Sum of interrupt program proceeding time
processed during 1 scan
iii. PLC internal processing time = Self-diagnosis time ＋ I/O refresh time ＋
Internal data processing time ＋ Communication service processing time
b. Scan time depends on whether to execute interrupt program and communication
processing.
Type
MPU processing time Expansion interface processing time
Executing ladder
(4Kstep)
PLC internal
processing time
Comm. module (main/expansion)
(200 byte, 1 block)
“E” type 5.4 ㎳ 1.0 ㎳ 0.5 ㎳
Remark
1) Momentary power failure?
This means the supply voltage at power condition designated by PLC is lowered below the allowable
variable range for a short time (some ms ~ some dozens ms). This interruption is called ‘momentary
power failure’.
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