Watlow PM PLUS™ 6
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Chapter 10 Appendix
Modbus
®
Programmable Memory Blocks
The Modbus
®
assembly or programmable memory blocks consists of 40 pointers to the parameters of your
choosing starting at Modbus
®
register 40 (shown on the following page). The pointers are 32-bits long and
are stored in two sequential registers. As an example, to move an alias to the analog input of the PM (register
360) into pointer registers 40 and 41, a single multi-write command (0x10 function) would be used writing
360 into register 40 and 361 into register 41.
The screen shot above was taken from a Watlow application called "Modbus
®
TCP Diagnostic Program for
EZ-ZONE PM, RM and ST", which can be found at http://www.watlow.com/en/resources-and-support/Techni-
cal-Library/Software-and-Demos by searching "Modbus
®
."
Once the parameters have been defined and written to the specified pointer registers, the working registers
will then represent the parameters written. In the example here, the 32-bit floating point analog input (360 and
361) was first written to registers 40 and 41 which defines working registers 200 and 201 as Analog Input 1.
As can be seen in the far right-hand column in the screenshot above, reading back registers 200 and 201, the
temperature as detected by the first analog input is displayed.
Note: Modbus
®
allows a maximum of 125 16-bit registers to be read with one read command. That is 62 of the 32-bit
registers defined here. Use two read commands to read the entire assembly if desired in one module. Each module has
its own assembly and the assembly working addresses must be within the same module.
