Important Points In Computer Link - Mitsubishi Electric FX3U-232-BD User Manual

FX Series PLC User's Manual - Data Communication Edition
Computer Link
6.2

Important Points in Computer Link

This section explains important points to be understood before creating programs for computer link.
6.2.1 Operations of PLC caused by data transfer
The PLC operations and scan time using computer link are as described below.
1. While the PLC is in RUN mode
For requests from the computer, the PLC executes access for one request during each END processing.
Sending and receiving are executed as interrupts.
Accordingly, when sending and receiving are executed, the scan time is longer by about 10%. The scan time
can be checked in D8010 to D8012 in the PLC.
2. Condition in which the transfer sequence in the PLC is initialized
The transfer sequence in the PLC is initialized in the following cases:
- When the power is turned ON
- When regular sending/receiving is completed
- When the control code "EOT" or "CL" is received in each format
- When the control code "NAK" is sent
- When the time-out time setting is detected
3. Occurrence of framing error in the computer
When a commercial interface in accordance with RS-485 is used in the computer, a framing error may occur
while nothing is sent from the PLC to the computer depending on the interface in the computer.
To cope with this nonconformity, let the computer ignore any data until the PLC sends STX, ACK or NAK.
4. Response of "NAK" from the PLC
When an error is detected, the PLC sends NAK to the computer.
5. Command sending from the computer
When sending commands from the computer to the PLC, wait for the interval times in the following table or
more after the PLC finishes receiving data in response to the previous command, and then send the next
command.
FX , FX
2N 2NC
FX (FX), FX
2 2C
D-46
For details on the time-out time setting, refer to Subsection 6.4.4.
PLC
FX , FX
3U 3UC
, FX , FX , FX
3S 3G 3GC
, FX , FX , FX , FX
0N 1S 1N 1NC
Interval times
300 s
100 s
two scan times
6 Control Procedures and Setting Methods
6.2 Important Points in Computer Link