The I/O bus imposes restrictions on the number of devices that can be connected to the bus and what type of devices that are allowed on certain positions.
The following restrictions apply to the I/O bus:
Position 1 reserved for a power supply
Position 2 reserved for AS-P or Automation Server
Maximum one AS-P or Automation Server per I/O bus
Maximum 32 devices per I/O bus
Even when connected by an S-cable, no more than 32 devices are allowed on the I/O bus.