What this module is
The ABB CI590 order code 1SAP221100R0001 is a distributed-automation interface module that sits on the CS31 fieldbus as a slave and adds 16 configurable digital I/O channels to the controller, with media redundancy built into the CS31 link. All 16 channels are software-configurable as input or output; the output stage is transistor (DC) with a per-channel drive of 0.5 A, so the module covers mixed discrete I/O on one node instead of forcing the panel builder to split DI and DO across two. Supply is 20.4... 28.8 V DC at the module terminals, which matches a standard 24 VDC control cabinet and tolerates the sag you see on long runs feeding a remote I/O island. Input voltage on the DI side is 24 V DC at 5 mA per point with a signal-exchange window of 0.1... 32 ms, so any input filtering or pulse-stretching has to be set inside that envelope. The module carries IP20 — it is a back-of-panel device, not a field-mounted island. Anything that lives outside an enclosure, in a wet well or under a hose, needs to go in a sealed cabinet first.
Second-source vs the DC532
Closest functional peer is 1SAP240100R0001 (DC532): 16 configurable DI/DO at 24 VDC 0.5 A, supply 20.4–28.8 V DC, IP20, signal-exchange 0.1–32 ms — plus 16 fixed 24 VDC digital inputs the CI590 lacks. If the panel used both the configurable bank and the 16 fixed inputs on the DC532, the CI590 swap drops those fixed inputs and the I/O map must be reworked. If only the configurable bank was used, the swap is mechanical.
Integration notes
Wire the 24 VDC feed within the 20.4–28.8 V window and ground the shield at the cabinet end only — the CS31 link is media-redundant, so the second path needs the same segregation from the primary to actually carry traffic on a break. Output transistor sourcing is 0.5 A per channel; sum the channel loads against the module's supply budget before paralleling outputs, because the listed 0.5 A is the per-point figure, not a package total.