Configuring the Bridge
38
3.8Setting theMapping:ModbusPlusto TCP/IP
Eachmessage fromaModbusPlusnode containsafive--byteroutingpathfield
(See Section 3.7).The bridge usesthe third bytetoindexintoitsTCPMapping
table,extracting an IPaddress fromthatentry.
Youcan edit the tabletomap the ModbusPlusrouting path’sthird bytetospecific
IPaddressesinyourapplication.
3.8.1TCPMapping TableLayoutandDefaultEntries
The TCPMapping tablecontains255 fields,labeled TCP_1 through TCP_255.
Thesefieldsdefine IPaddressesformessages(from ModbusPlusnodes)which
contain1through255 decimal in byte3ofthe ModbusPlusmessage routing path.
Bydefault the bridge automatically setsthe first three bytesofeachIPaddress to
matchthe first three bytesof the bridge’sIPaddress.(SeeFigure 14 and Section
3.4.3foran example ofconfiguring the bridge’sIPaddress.)Thebridge setsthe
fourth byte of the IPaddress mapping tothe range 1 ... 255.
Forexample,ifyou configurethe bridge’sIPaddressas:
205.167.7.65
the TCPMapping table’s255locationswill automaticallydefault to:
TCP_1:205.167.7.1
TCP_2:205.167.7.2
... ...
TCP_255:205.167.7.255
Figure18showsan example of typicaldefaultTCPmapping,with one custom
routing entrymade bythe user.