Revision 6    HC900 Process & Safety Controller User and Installation Manual  29 
21 April 2017 
Controller Module 
C30 and C30S, C50 and C50S, C70 and C70S, C75 and C75S Controllers share the same features, with exceptions 
noted. 
CPU model number (C30 and C30S, C50 and C50S , C70 and C70S, C75 and C75S). 
Lithium battery (battery tray), which is readily accessible for field replacement. Battery tray on 
Controllers C30/C30S, C50/C50S, C70/C70S, and C75/C75S. 
Serial Interface Ports 
For legacy systems, two serial ports, S1 and S2, each configurable as RS-232 or RS-485 provides 
interfaces to a PC, external modem, Modbus devices or Operator Interfaces. 
For new systems, two galvanically isolated RS-485 serial ports, S1 and S2 provide interfaces to PC 
using RS-485 to usb cable.  External modem or Modbus devices may be interfaced using RS-485 to 
RS-232 converter. RS-485 interfaces to PC, Control Stations or Modbus devices/host. 
Ethernet LED status indicators 
for communications functions 
Figure 12 – Controller Module 
Connection to I/O port of 
Scanner Module. 
C50/C50S/C70/C70S, 
C75/C75S only  
Second Ethernet (E2) Host 
Connection to PC applications 
or peer HC900 controllers. 
C70/C70S/C75/C75S only 
First Ethernet (E1) Host 
Connection to PC applications 
or peer HC900 controllers 
LED status/diagnostic indicator 
for serial port S2 (left) 
LED status/diagnostic indicator 
for serial port S1 (right) 
LED status/diagnostic indicator 
for controller module 
Mode switch (Pgm, Run/Pgm, 
Run). Not present on 
C75/C75S; see RSM 
 
Redundant controller rack contains two C75s or C75Ss. Left CPU is designated CPU-A, right CPU is CPU-B; either 
CPU can be Lead.