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13.2.4 Explicit Messaging Tag Reference
When class 3 (explicit messaging) connections are used, register contents are
read from and written to the interface card via Ethernet/IP by reference to “tag
names”. Tags are read via the Ethernet/IP “data table read” service, and tags
are written via the Ethernet/IP “data table write” service. Different tags exist for
reading vs. writing.
Any given register can be accessed with its own unique tag name, or an array
tag can be used to access a group of registers with one PLC instruction. Tag
names are generated according to the following structure:
[action prefix][_reg_][register number]
Where
[action prefix] is a 2-character field, and is equal to either “rd” for read tags, or
“wr” for write tags. Although commonly followed for naming clarity, this “read
vs. write” naming convention is not strictly enforced by the interface card,
however: it is perfectly acceptable to write to a tag that starts with “rd” and read
from a tag that starts with “wr”.
[_reg_] is just the 5-character sequence “_reg_”.
[register number] is a 1- to 4-character field (“1”, “2”…”1484”, “1485”)
corresponding to the referenced register number.
Examples
Read “acceleration time 1” (register #10)....................................rd_reg_10
Write “option frequency command” (register #1008)...................wr_reg_1008
Read “inverter status 1” (register #1402) ....................................rd_reg_1402
Additionally, a few special tags exist which provide backward-compatibility with
V1.000 network interface CPU firmware. These are specified in Table 3.
Table 3: Special Tag Reference
Service Tag Name Register Start Same As…
Data table read rd_reg_basic 1 rd_reg_1
Data table read rd_freq_out 1401 rd_reg_1401
Data table read rd_inv_stat1 1402 rd_reg_1402
Data table read rd_torq_out 1419 rd_reg_1419
Data table read rd_inv_stat2 1443 rd_reg_1443
Data table write wr_reg_basic 1 wr_reg_1
Data table write wr_cmd1 1007 wr_reg_1007
Data table write wr_freq_cmd 1008 wr_reg_1008
Data table write wr_cmd2 1024 wr_reg_1024
Data table write wr_torq_cmd 1034 wr_reg_1034