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Concept

Concept


Products: AO-8, AO-V-8, AS-P-3, DI-16, DO-FA-12, DO-FC-8, AS-P, PS-24V, RTD-DI-16, UI-16, UI-16 v2, UI-8/AO-4, UI-8/AO-4 v2, UI-8/AO-V-4, UI-8/AO-V-4 v2, UI-8/DO-FC-4, UI-8/DO-FC-4 v2
Functionalities: Central IO , Hardware
Product version: 7.0, 7.1
6/25/2026

I/O Bus Parts

The I/O bus consists of the following parts:

  • Power bus

  • Address bus

  • Communication bus

The figures below and the following sections describe the I/O bus parts with two examples based on the automation server model connected to the bus:

  • AS-P server

  • AS-P-3 server

 
action_zoom_plus_stroke I/O bus parts, example with AS-P server
Figure: I/O bus parts, example with AS-P server
 
action_zoom_plus_stroke I/O bus parts, example with AS-P-3 server
Figure: I/O bus parts, example with AS-P-3 server
Power bus

The power bus distributes 24 VDC power either from a PS-24V power supply to an AS-P server and Central IO modules or from an AS-P-3 server to Central IO modules.

Use the power budget for the PS-24V power supply to calculate the maximum number of devices that the power supply can supply. For more information, see Power Budget . If more devices are used, additional power supplies must be added to the I/O bus.

Use the power budget for the AS-P-3 server to calculate the maximum number of devices that the automation server can supply. For more information, see Power Budget for AS-P-3 Servers . If more devices are used, PS-24V power supplies must be added to the I/O bus.

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 and to the next terminal base on the I/O bus. This applies to the PS-24V power supply, the AS-P server, and the Central IO modules. The AS-P-3 server differs in that it is a one-piece device, without a terminal base, but the address bus is used in the same way to pass on the address to the next device 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 .

Table: Positions and Module IDs, Example with AS-P Server

Device

Physical Position Number

EcoStruxure Building Operation Module ID

Power Supply

1

Number is hidden in WorkStation

AS-P server

2

Number is hidden in WorkStation

Central IO module

3

3

Central IO module

n

n <=32

Table: Positions and Module IDs, Example with AS-P-3 Server

Device

Physical Position Number

EcoStruxure Building Operation Module ID

AS-P-3 server

2a

Number is hidden in WorkStation

Central IO module

3

3

Central IO module

n

n <=32

  1. Position 1 is reserved for a power supply. Position 1 is not used as the AS-P-3 server has a built-in power supply.
Communication bus

The communication bus enables serial (RS-485) communication between the automation server and the Central IO modules. The automation 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.

Note:

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.

See Also

  • Terminal Bases
  • PS-24V Power Supplies
  • AS-P Servers
  • AS-P-3 Servers
  • I/O Bus
  • I/O Bus Limits
  • Device Addressing
  • Backplane Board
  • Power Budget
  • Power Budget for AS-P-3 Servers
  • Configuring an I/O Module