42 HC900 Process & Safety Controller User and Installation Manual Revision 6
21 April 2017
Serial Ports
(RS-232 and RS-485 for legacy systems and two galvanically isolated RS-485 ports for new
systems)
Overview
Figure 22 – Controller Serial Ports
For Legacy systems, the S1 default setting is RS-232; S2 default setting is RS-485. Each port can be set
to RS-232 or RS-485 (see page 43). For RS-232 cable connections see page 134. For RS-485
connections see page 152.
For new systems, either of two ports S1 and S2 can be configured as RS-485. For SIL applications
communication cable shield connection must be made to IO grounding bar instead of the connector
shield connector.
Ports configurable as ELN (default) or Modbus RTU.
Controller can act as Modbus master or slave through either port.
Controller can be slave to masters such as
On Legacy systems- Operator Interface (1040, 559). Must be on galvanically isolated RS-485 port S2.
Honeywell HC Designer PC software
Third party PC HMI software
Third party Operator Interface
Controller can be master to slaves such as
Any Honeywell Modbus device (e.g., recorders, controllers, flame safety)
Any non-Honeywell Modbus device.
Only one master port at a time; can’t have both serial ports as master ports.
Modbus master ports default to slave ports, ELN protocol when CPUs are in Program mode.
Baud rates to 115,200
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