Rockwell Automation 2711P Creating Modbus Applications - Manual (Page 66)

Publication 2711P-UM002B-EN-P - March 2007
66 Modbus/TCP Address Definitions
String Support
The Modbus model supports reading and writing holding register
memory as an ASCII string. When using holding registers for string
data, each register will contain two bytes of ASCII data. The order of
the ASCII data within a given register can be selected when the string
is defined. The length of the string can be 2 to 240 bytes and is
entered in place of a bit number. The length must be entered as an
even number. The byte order is specified by appending either an H or
L to the address.
String Example:
To address a string starting at 40200 with a length of 100 bytes and
HiLo byte order enter:
40200.100H
Arrays
Arrays are also supported for the holding register addresses. The
syntax for declaring an array (using decimal addressing) is 4xxxx[cols]
with assumed row count of 1 and 4xxxx[rows][cols].
For Word, Short and BCD arrays, the base address + (rows * cols)
cannot exceed 65536.
For Float, DWord, Long and Long BCD arrays, the base address +
(rows * cols * 2) cannot exceed 65535.
For all arrays, the total number of registers being requested cannot
exceed the holding register block size that was specified for this
device.