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Products: AO-8, AO-V-8, DI-16, DO-FA-12, DO-FC-8, AS-P, PS-24V, RTD-DI-16, UI-16, UI-8/AO-4, UI-8/AO-V-4, UI-8/DO-FC-4
Functionalities: Central IO , Hardware
Product version: 3.3, 2022, 2023, 2024

I/O Bus Parts

The I/O bus consists of the following parts:

  • Power bus

  • Address bus

  • Communication bus

action_zoom_plus_stroke I/O bus parts

I/O bus parts

Power bus

The power bus distributes 24 VDC power from the power supply to the AS-P server and the Central IO modules.

Use the power budget to calculate the maximum number of devices that the power supply can supply. If more devices are used, additional power supplies must be added to the I/O bus.

For more information, see Power Budget .

Address bus

The address bus is used to pass the address from the terminal base backplane to the electronics module that is installed on the terminal base to the next terminal base on the I/O bus. Typically, the physical position (address) of the devices on the I/O bus should match the module IDs in the EcoStruxure Building Operation software. For more information, see Device Addressing .

Electronics Module

Physical Position Number

EcoStruxure Building Operation Module ID

Power Supply


Number is hidden in WorkStation

AS-P server


Number is hidden in WorkStation

Central IO module



Central IO module


n <=32

Communication bus

The communication bus enables serial (RS-485) communication between the AS-P server and the Central IO modules. The AS-P server controls and supervises the communication on the communication bus. The Central IO modules also monitor their communication status. When a new Central IO module is configured and connected to the I/O bus, the automation server automatically detects the new Central IO module.


All the buses use a common ground, which is connected to the signal return paths with terminals called “RET”. The signal return path is also called signal ground.

  • Terminal Bases
  • I/O Bus
  • I/O Bus Restrictions
  • Device Addressing
  • Backplane Board
  • Power Budget
  • Configuring a Central IO Module