AERCO Modbus Communications Manual - Manual (Page 53)

Chapter 3
MODBUS
Communication GF-114
Standard Application Operations USER MANUAL OMM-0035_0C
05/18/12 AERCO International, Inc. • 100 Oritani Dr. • Blauvelt, NY 10913 • Ph: 800-526-0288 Page 53 of 200
CHAPTER 3. STANDARD APPLICATION OPERATIONS
3.1 INTRODUCTION
This Section describes the standard application operations for AERCO C-More Boiler
Controllers and the AERCO Boiler Management System (BMS/BMS II), and the AERCO Control
System (ASC) and how they are achieved utilizing Modbus. Paragraphs 3.2 through 3.2.7
provide information for the C-More Boiler Controllers which can only function as Slaves in a
Modbus Network. Paragraphs 3.3 through 3.3.4 provide similar information for the BMS, BMS
II, and ACS, which can function as either a Master or Slave in a Modbus Network.
NOTE
Additional information on Modbus hardware and software set up
and installation are provided in Section 4 and Section 5 of this
manual.
3.2 C-MORE CONTROLLER STANDARD APPLICATION OPERATIONS
The information in the following paragraphs apply to C-More Boiler Controllers with the following
exceptions:
• C-More Boiler Controllers utilize a Fixed 10 second “Heartbeat” timer.
• C-More Boiler Controllers, require temperature readings to be converted from “counts” to
°F or °C.
3.2.1 Password Protection for Input and Holding Register Access
Access to the C-More Input Register and Holding Register addresses are protected via security
level passwords. Two separate Holding Register addresses (0x0002, 0x0003) are assigned for
password entries, one for the Modbus (RS485) Network and one for the RS232 front panel user
interface. If desired, separate security passwords can be entered for each interface.
Each C-More Controller menu parameter is assigned a preset security level that controls access
from the front panel user interface. If the current communication password of the front-end
software does not match the C-More Slave addresses security level, access is denied. When
this occurs, an Illegal Data Address Exception Code (02) is generated and the data is not
changed. If a Modbus message is received to read multiple Input or Holding Registers
(Function Codes 03 or 04) and one or more of the register addresses is not accessible, an
Illegal Data Address Exception Code will also be generated and no data is supplied to the
Master. It should be noted that Modbus “Write Multiple Registers” command (Function Code
16) is not supported by AERCO C-More Controller Slaves and will cause an Illegal Function
Exception Code to be generated.
The Holding Register data can be viewed without a password. However, the data cannot be
changed without entering the appropriate password. The communications port security
operation will mirror the security operation for viewing and adjusting parameters via the front
panel keypad. Refer to C-More Operation Manual GF-112 for additional information on security
passwords and menu access.