Micromod MOD: 1800P - MOD 30ML Identity Module (Version 2) System, I/O and Communications Functions - Manual (Page 245)

Logic Functions - Book 1
APPENDIX B - MODBUS MASTER CONFIGURATION
B-1
APPENDIX B
MODBUS MASTER CONFIGURATION
B.1 OVERVIEW
Modbus Master communication functionality was introduced on the MODCELL Multiloop
Processor firmware (version 3.1 logic controller, version 2.1 regulatory controller) without
adding any new function blocks. This has been accomplished by adding new code and making
changes to the existing firmware in the MODCELL Serial Communication (MSC) (formerly
known as the Modbus Slave Communication) and Expression (EX) blocks. The attributes for
these blocks have not been changed in any way that required changes in the Application
Builder version 1 (the 1706S version 5.0B may be used as a configuration tool when at this
version level). Extended Modbus, requires the Application Builder version 2 or later software.
A MODBUS configuration requires a MSC block that is to be used as a MASTER and EX
blocks that are used to control reading and writing of data to any number of Modbus Slave
devices. The following MODBUS features are available:
RTU mode of transmission
Function codes:
1 Read Coil Status
2 Read Input Status
3 Read Holding Registers
4 Read Input Registers
5 Force Coil*
6 Preset Single Register*
15 Force Multiple Coils*
16 Preset Multiple Registers*
* Supports Global Writes.
Communication Parameters:
Slave Addr 1 to 247
Parity None, Odd, Even
Stop Bit 1 or 2
Baud Rate 150 to 38.4K
Communication Type:
RS232 2 Slot
RS485 1 Slot 2 Wire
RS485 2 Slot 2 Wire
RS485 2 Slot 4 Wire
When an RS485 communication bus is being used, the Modbus Master is responsible for
providing pull-up and pull-down resistors which will keep the bus in a MARK/IDLE state when
all the transmitters are tri-stated. Modbus Network installation instructions can be found in
IB-23C600 Issue 5 or later.