B1-6
IM 34M06H62-02E 3rd Edition : Jul.16
2015-00
B1.3 Writing and Reading after Powering On
Do not read from and write to I/O data registers before module startup completes. This
can be ensured by checking that the MDLRDY relay is set.
Table B1.4 Relays Related to Writing after Powering On
Input Relay Number
Xnn
*1
Symbol Description Data Values
X16 MDLRDY Module startup has completed
0: During startup,
1: Startup completed
*1: denotes the slot number where the module is installed.
Figure B1.2 Checking for Module Startup Completion after Powering On
After power on, it takes up to approximately 2 seconds for the module startup to complete
(startup initialization). Any data written during this period may be ignored. For instance, if
a write instruction to the special relay M35, “On for 1 Scan after Program Start” is used in
a sequence program to start a program after power on, the written data may be ignored.
If data is written before the MDLRDY relay turns on, such data may be overwritten during
module initialization. If data is written for a stored parameter, the data may be overwritten
by stored data; if data is written for a non-stored parameter, the data may be overwritten
by its default parameter value.
Similarly, if data is read before the MDLRDY relay is set, the data read may be invalid.
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