Rockwell Automation 1785-KA5P/B DHP COMM. ADAPATER MOD. - Manual (Page 35)

Communicating through the 1785ĆKA5
Communication Adapter Module
Chapter 3
3-7
How the 1785ĆKA5 Module Operates as a Gateway
The 1785-KA5 module operates as a gateway when attached DH485
stations do not fully implement IP. It converts IP packets to DH485 local
packets and sends them to their DH485 destination stations.
Important: SLC 5/01, SLC 5/02 and fixed controllers do not support IP.
DH+ devices that wish to send packets to DH485 devices that do not
implement IP protocol must address the 1785-KA5 DH+ or DH485
gateway service internet address (You set these addresses before you
install the 1785-KA5 module. See page 2-7.)
The 1785-KA5 communicates with DH+ devices using IP and DH485
devices using DH485 packets only. The 1785-KA5 module automatically
converts between the DH+ and the DH485 as necessary. Neither side is
aware of the packet conversion process.
Only devices that fully implement IP protocol may initiate PCCC
command packets. DH485 devices that do not implement IP may only send
reply packets.
Internet Protocol SingleĆhop Packets
The IP “single-hop” packet is a special type of IP-to-DH485 remote packet
where the DH+ device sending the packet believes it is connected to a
gateway that only has two networks – the network it is connected to, and
its opposite network.
A single-hop packet is formatted like an IP remote data packet, except that
the destination (DST) and source link (S_LINK_ID) fields are zero, so the
packet is not routed using the normal IP routing algorithm. When the
1785-KA5 module receives the packet, it automatically retransmits the
packet on the network opposite the one on which the packet was received.
Important: The 1785-KA5 module will accept single-hop packets from its
DH+ side only (no DH485 software can generate these packets.) New
software running on DH485 devices wanting to send packets off of the
DH485 network should only implement full IP-formatted packets – not
single-hop packets.