Rockwell Automation 57C442 Data Highway Plus Interface Module - Manual (Page 31)

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4.2.6 Off-link Routing Paths
This section describes using a Data Highway network as a bridge to link
two Data Highway Plus networks using A-B 1785-KA modules. If you
need information about other bridge networks, refer to A-8
documentation.
The routing information is added to the “slave_reg” parameter of the
GATEWAY_CMD_OK@ function. A leading exclamation mark (!) is
used to signify that routing information is included. The routing
information is added to the beginning of the string as hexadecimal
bytes separated by periods. See figure 4.10.
For a 1785-KA Data Highway bridge, the twelve routing bytes are:
where:
DID is the destination node’s link ID; see A-B documentation. This is
0 for a 1785-KA bridge.
DNDE is the station address of the destination on the destination link.
For the Data Highway bridge, only the low byte is used. It consists of
the upper two bits of the Data Highway address of the remote bridge
1785-KA and the lower six bits of the Data Highway Plus address of
the final Data Highway Plus station.
SID is the link ID of the local network; see A-B documentation. This is
0 for a 1785-KA bridge.
SNDE is the station address of this station on the local Data Highway
Plus network.
4.2.6.1 Example of Bridging Two Data Highway Plus Networks
using 1785-KA modules
In the following example, the Data Highway Plus Interface module is
station 24 octal on a Data Highway Plus network. The first 1785-KA
bridge module is at address 42 octal on the Data Highway Plus network
and 142 octal on the Data Highway network. The remote bridge module
is at station address 240 octal on the Data Highway network and 40
octal on the Data Highway Plus network. The final destination node is
at station address 4 on the remote Data Highway Plus network.
Byte Value Meaning
1 LSAP 1 for a 1785-KA bridge
2 24h
3 DID_LO see below
4 DID_Hl see below
5 DNDE_LO see below
6 DNDE_Hl see below
7 LIFETIME 80h for a 1785-KA bridge
8 SID_LO see below
9 SID_Hl see below
10 SNDE_Hl see below
11 SNDE_LO see below
12 NSAP0 for a 1785-KA bridge
Figure 4.10 – Off-link Message Routing Bytes