User guide

1–3Network Layers
Publication 17706.5.16 - October 1996
DH Link
A DH link is a local area network (LAN) designed for factory-floor
applications. This link accepts 64 devices and can transmit 57.6 K
bits of data per second.
A DH link consists of a trunk cable up to 10,000 feet (3,048 meters)
long and drop cables as long as 100 feet (30.48 meters) each.
Each node is at the end of a drop cable and connects to the DH link
through a station connector (cat. no. 1770-SC). This is the only
configuration tested and supported by Allen-Bradley.
This processor Connects to a DH link through the
PLC2 family
DH PLC2 family communication adapter module
(cat. nos. 1771KA2, KG)
PLC3
DH PLC3 family communication adapter module
(cat. nos. 1775KA,S5, SR5)
PLC5/250
Resource manager module
(cat. nos. 5130KA, RM1,RM2)
PLC5, SLC 5/04
➀
DH+/DH communication module
(cat. no. 1785KA)
➀
Although a PLC5 processor does not directly connect to a DH link, it can communicate with
devices on a DH link via the 1785KA module.
A DH link implements peer-to-peer communication through a
scheme called the floating master. With this arrangement, each
node has equal access to become the master. The nodes bid for
temporary mastership based on their need to send information.