IAI America XSEL Ethernet - Manual (Page 24)

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4.4 Correspondence of Modbus/TCP Address and X-SEL I/O
Modbus/TCP can address the same object using either bit addressing or word addressing.
The DI area (bit numbers from No. 0 up to No. 299 can be defined) of the X-SEL controller is mapped
in the word address 0x400 (1024) (coil and holding register as viewed from the PC side) under
Modbus/TCP.
The DO area (bit numbers from No. 300 up to No. 599 can be defined) of the X-SEL controller is
mapped in the word address 0x000 (0) (input discrete and input register as viewed from the PC side)
under Modbus/TCP.
Since the DI addressing in the X-SEL controller and the addressing via Modbus are different, it is
important to note the following two points:
1. The number order of one byte in the byte boundary is reversed.
(Example)
X-SEL DI7
 Modbus bit address 1 (Modbus/TCP bit address 0)
DI0
 Modbus bit address 8 (Modbus/TCP bit address 7)
2. When register access is executed from the X-SEL controller using an IN, INB, OUT or OUTB
command, the upper and lower bytes will be reversed.
(Example)
Writing 0x1234 to 16 bits from X-SEL DO300
 Modbus input register 0 (Modbus/TCP bit address 0)
DI0
 Modbus bit address 8 (Modbus/TCP bit address 7)
Both the Motorola and Intel formats can be supported using an FMIO command. (Refer to Chapter 2,
“Explanation of Commands,” in the operation manual for the X-SEL controller.) The FMIO command
changes the endian in IN/OUT commands. Executing input or output after an FMIO command
execution with the format type set to “1” will align the byte order with Modbus/TCP. Each FMIO
command is valid only with respect to the task for which the command is executed.
A table of correspondence is shown on the next page.