Siemens SIMATIC TI525 Hardware And Installation Manual page 60

Do not install more than four word modules in a physical base.
This may cause a DC loading problem in the PLC which could
result in unexpected disabling of output modules (including
discrete output modules). For example, even though a 16-slot
base contains two logical bases, you can only have a total of four
modules.
Appendix C gives the power requirements for many of the currently available
Series 505 and Series 500 modules. For other modules not listed see the manual
for that module.
All the TI525 and TI535 controllers use the Series 505 I/O modules. These I/O
modules have different numbers and types of I/O points. For example, an
eight-point discrete input requires eight inputs (Xs) be assigned, while an
eight-point analog output module requires assignment of eight word outputs
(WYs). Table 3-2 lists the number and type of points required to log in the Series
505 I/O modules. Additional information on particular modules is given in the
manual included with each module.
Hardware and Installation User Manual
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INSTALLATION
NOTE
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