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MELSEC-Q
8 COMMUNICATION WITH INTELLIGENT FUNCTION MODULE/SPECIAL
FUNCTION MODULE
8.3.4 Effects of quicker access to the special function module and countermeasures against
them
(1) Effects of quicker access to the special function module
As the scan time of High Performance model QCPU increases, there are some
limitations for the execution of the FROM/TO instruction to the AnS-compatible
special function module.
The following effects may be produced in the program which reads/writes data
from/to a special function module with the FROM/TO instruction at every scan:
(a) Special function modules which assign priority to the FROM/TO instruction
1) When the FROM/TO instruction is executed, the special function module
stops its processing and processes the FRO/TO instruction first.
As a result, the processing time of the special function module becomes
longer, resulting in watch dog timer error of the special function module.
2) The followings are the special function modules which assign priority to
the FROM/TO instruction.
• A1S64AD, A1S68AD
• A1S62RD3, A1S62RD4
• A1S68DAV, A1S68DAI
• A1S68TD
• A1SD75P1(-S3), A1SD75P2(-S3), A1SD75P3(-S3)
• A1SD75M1, A1SD75M2, A1SD75M3
(b) Special function modules which suspend processing of the FROM/TO
instruction
1) Even when the FROM/TO instruction is executed, the special function
module continues its processing and suspends processing of the
FROM/TO instruction until the processing is completed.
As a result, the scan time becomes longer by the period to wait the
completion of the processing of the special function module.
2) The following are the special function modules which suspend the
FROM/TO instruction.
• A1S63ADA, A1S66ADA
• A1SD61, A1SD62, A1SD62D, A1SD62E
• A1SD70, A1SD71-S2, A1SD71-S7
• A1SJ71PT32-S3, A1SJ71T32-S3
• A1SD51S
• A1SJ71ID1-R4, A1SJ71ID2-R4
(2) Countermeasures against the effects of quicker access to the
special function module
To use a special function module with High Performance model QCPU, adjust
the execution time with SM415 (2n-ms clock) and SD415 (2n-ms clock setting).
The initial value of SD415 is "30." When SD415 is used for interlock of the
FROM/TO instruction, the FROM/TO instruction is executed at every 120 ms.
SM400
SM415
MOVP K30 SD415
FROMP H0 K1 D0 K1
REMARK
1) To change the clock value of SM415, store the new value in SD415.
2) For details of SM415, see appendix 1. For details of SD415, see appendix 2.
