Scan Synchronization Specification - Mitsubishi Electric MELSEC-Q Series User Manual

8.3.5

Scan synchronization specification

Whether to synchronize the link scan with the sequence scan of a CPU module or not can be selected.
Selecting the asynchronous mode shortens input transmission delay time. Selecting the synchronous mode shortens
output transmission delay time.
(1) Difference between the asynchronous and synchronous modes
Item
Asynchronous mode
Synchronous mode
When a module is operated in the synchronous mode, the L RUN LED may turn on dimly.
(2) Precautions
(a) Sequence scan time when the synchronous mode is used
Do not exceed the following time. If the time exceeds the one listed below, a timeout error occurs in each
station.
(b) When an A(1S)J61BT11/A(1S)J61QBT11 is connected as a local station in the
synchronous mode
Pay attention to the following notes when an A(1S)J61BT11/A(1S)J61QBT11 is connected as a local station in
a system with a QJ61BT11N as a master station.
• When an A(1S)J61BT11/A(1S)J61QBT11 is connected as a local station, adjust the sequence scan time
of the local station side so that the sequence scan time of the CPU module in the local station becomes
longer than ST. For ST, refer to Page 366, Appendix 4.1.
• When an A(1S)J61BT11 is connected as a local station, use XnC as an interlock of the FROM/TO
instructions on the local station side.
When an A(1S)J61BT11/A(1S)J61QBT11 is connected as a local station in a system with a QJ61BT11N as a master station,
using the asynchronous mode is recommended. To use the synchronous mode, pay attention to the notes described above.
A link scan is performed asynchronously with the sequence scan of a CPU module. Select this
mode to shorten input transmission delay time when a sequence scan takes much longer than a
link scan. Note, however, that the output transmission delay time is shortened.
Data link is performed with a scan synchronizing a program. (The sequence scan and link scan
start simultaneously.)
Select this mode to shorten output transmission delay time. Note, however, that the input
transmission delay time becomes longer if a sequence scan takes much longer than a link scan.
Because a link scan synchronizes a sequence scan, extended sequence scan time increases link
scan time.
Transmission speed
10Mbps
5Mbps
2.5Mbps
625kbps
156kbps
CHAPTER 8 FUNCTIONS
Description
Sequence scan time
50ms
50ms
100ms
400ms
800ms
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