You should consider D series Modbus RS485 Digital IO modules. Because they let you read contacts with spare Modbus RS485 ports for status monitoring.
Modbus RS485 Contact Monitoring
The D series is a versatile family of Modbus RS485 I/O modules. Because a Digital I/O solution is available for many contact monitoring and actuation applications. The supply voltage range is a wide 10 to 30Vdc (DIN rail unit 5Vdc), as well as Modbus compatibility with a number of software options.
When you have spare a spare RS485 port, and need to add contact monitoring, use D series contact monitoring modules. Because D series Modbus RS485 Digital I/O modules allow the simple monitoring of industry standard contacts. They use the standard Modbus protocol. So you can easily connect your existing sensing devices to modern control systems. They are a simpler way to add sensor measurement to a RS485 bus than other types. Because they read common sensor signals, they are in many cases used in HVAC systems, refrigeration systems, chillers, environmental monitoring, computer room monitoring, dryer, and a variety of other applications.
When you need simple to use a Modbus RS485 contact monitoring module, use the D series. In other words D series Modbus RS485 Digital IO modules are a simple way to add contact monitoring to a RS485 bus.
D Digital IO
Input: digital signals 0-30Vdc, may monitor dry contacts via internal pull-up resistor.
Output: open collector can pull up to +30Vdc, drive up to 30mA loads (DIN rail unit 100mA)
Count: part number dependent (factory set).
Connectors: Screw terminal barrier plug (supplied).
Surface Mount: Screw threads: 6 X 32, spacing: 2.700″ (6.858 cm), with captive hardware.
Rail Mount: DIN 35mm
171 DIN rail mounted 6 digital input module
172 DIN rail mounted 6 digital output module
1702M surface mounted 7 digital input 8 digital output IO module