ABB AC 900F Mounting And Installation Instructions Manual page 29

Section 3 Modules
Coupler bus C1-C2_us.png
Unused slots must be covered with TA dummy couplers to comply with the ISA
74.01 G3 requirements.
I/O bus
The I/O bus on the right side of the PM CPU module is provided for communication
with I/O modules that are directly connected to the CPU module. This bus serves for
exchanging I/O data and diagnostic data between the CPU module and the I/O
modules.
IO_Bus_us.png
M&I – AC 900F Controller
Interfaces
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