Operating instructions

PTQ-MCM ♦ Quantum / Unity Platform Reference
Modbus Communication Module
Page 100 of 139 ProSoft Technology, Inc.
April 29, 2008
The module transfers the entire read and write areas at the end of every
processor scan. The module will hold the processor scan for a certain period of
time, which allows the module to transfer the entire read and write areas. This
means that the larger the read and write areas, the longer the processor scan
time will be. Refer to Module Performance for more detailed information on
determining scan times.
Note: The diagram above shows the memory addresses for a Quantum / Unity processor. If you
are deploying the PTQ-MCM with a Unity processor, substitute %MW for read only data, and %IW
for read/write data.
8.2.2 Special Functions
Command control blocks are special blocks used to control the module or
request special data from the module. The current version of the software
supports four command control blocks: event command control, command
control, warm boot and cold boot.
8.2.3 Event Command
Event command control blocks send Modbus commands directly from the ladder
logic to one of the master ports. The format for these blocks is displayed below:
Write Block - Event Command
Offset Description Length
0 1000 to 1247 or 2000 to 2247 1
1 Internal DB Address 1
2 Point Count 1
3 Swap Code 1
4 Function Code 1
5 Destination Code 1
6 to 63 Spare 1
The block number defines the Modbus port to be considered. Block 1000
commands are directed to Port 1, and block 2000 commands are directed to Port
2. The slave address is represented in the block number in the range of 0 to 255.
The sum of these two values determines the block number. The parameters
passed with the block are used to construct the command.
 The Internal DB Address parameter specifies the module's database
location to associate with the command.
 The Point Count parameter defines the number of registers for the
command.
 The Swap Code is used to change the word or byte order.
 The Node Address parameter is used to define the device on the Modbus
network to consider.
 The Function Code parameter is one of those defined in the section
[Modbus Port 1 Commands].