Here are some exerpts from AB DF1 Command Set User’s Manual available at

Use this manual to:

• program a DF1 driver for a computer to interface to Allen-Bradley DF1 products and to proprietary networks via protocol bridges

• write applications for 1784-KT, -KT2, -KTX, -KTXD, -PCMK communication interfaces using standard Rockwell Software Inc. (RSI) driver products

• troubleshoot your network

Read this manual before you attempt to write a DF1 driver, or before attempting to troubleshoot your network. We assume that you are already familiar with:

• your serial device

• Allen-Bradley PLC processors

Before you begin writing your driver, make sure you have:

• a pocket calculator that adds, subtracts, multiplies, and divides in decimal, hexidecimal, octal, and binary

• a serial protocol analyzer for displaying actual hex bytes sent to and from a DH, DH+, or DH485 module

Related Publications
Publication Name Publication Number DH/DH+/DH II/DH485 Cable Installation Manual 17706.2.2 DH Overview Product Data 17702.39 DH+ Overview Product Data 17852.6 SCADA System Selection Guide AG2.1 SCADA System Application Guide AG6.5.8 Terms and Abbreviations R

Allen-Bradley offers a wide range of interfaces for the DH, DH+, and DH485 networks, including: Catalog Number Product Related Documentation 1747KE DH485/RS232 Interface Module 17472.3.7, product data 17476.12, user manual 1770KF2 DH or DH+ Asynchronous (RS232 or RS422A) Interface Module 17706.5.13, user manual 17706.5.13RN1 release notes 1770KF3 DH485 Asynchronous (RS232) Interface Module 17706.5.18, user manual 17706.5.18RN1, release notes 17706.5.18RN2, release notes 1771KA2 DH PLC2 Family Communication Adapter Module 17715.2, switch settings 17716.5.1, user manual 1771KG PLC2 Family RS232 Interface Module 17712.32, product data 17716.5.8, user manual 17716.5.8DU1, document update 1771KGM SCADA Communication Master Module for PLC2 Family 17712.85, product data 17716.5.39, user manual 1771KE,KF DH RS232 Interface Module 17716.5.16, user manual 17716.5.16DU1, document update 1775KA DH PLC3 Communication Adapter Module 17756.5.1, user manual 1775S5,SR5 PLC3 I/O Scanner Module 17756.5.5, user manual 1784KR DH485 Personal Computer Interface Module 17842.23, installation data 17842.23RN1, release notes 1784KT DH+ PC Interface Module 17842.31, installation data 1784KT2/B DH+ PS/2 Interface Module 17842.21, installation data 1784KT2/C 17846.5.16, user manual 1784KTX DH+ PC Interface Module 17846.5.22, user manual 1784KTXD DH+ PC Interface Module 1784PCMK DH+/DH485 PCMCIA communication interface 17846.5.19, user manual 1785KA DH/DH+ Communication Interface Module 17852.6, product data 17856.5.1, user manual 1785KA3 DH+ PLC2 Family Communication Adapter Module 17852.6, product data 17856.5.3, user manual 17856.5.3DU1, document update 1785KA5 DH+/DH485 Communication Interface Module 17856.5.5, user manual 1785KE DH+ RS232 Interface Module 17856.5.2, user manual 5130RM1,RM2 PLC5/250 Resource Manager Module 50006.2.1, design manual 50006.2.10, installation manual 9351AIX, DKTS, HPUS, OSF, VS, WES, WKTS 9355WABC INTERCHANGE Software RSLINX C SDK Software 50006.4.21, reference manual 9398WABCTD11.21.95, data sheet R

Network Layers Your network is made up of several layers, including: Physical layer transmits bits between communication devices. Datalink layer runs protocol to guard against errors, detects errors, and corrects errors. Packages data and puts it onto the physical cable. Manages the flow of the data bit stream into and out of each network node. Network layer establishes connections for communication between network nodes. Transport layer performs segmentation and reassembly of messages. Provides recovery from transmission errors. Session layer establishes and terminates network communications between applications. Presentation layer manages data formats for the applications. Application layer serves as the window through which applications access communication services, including file transfers, virtual terminal functions, and email.

Physical Layer
The physical layer is a set of cables and interface modules that provides a channel for communication between the nodes. A node is a connection point onto a network, typically containing a unique address. When you connect a computer serially to your DH, DH+, DH-485, or ControlNet link, the interface module acts as an interface between the:

• DF1 link (RS-232 or RS-422-A)

• network link (DH, DH+, DH485, ControlNet link) DF1 Link A DF1 link provides:

• master-slave communication through a half-duplex protocol

• peer-to-peer communication through a full-duplex protocol

This manual provides information necessary to write your own driver for an intelligent device on a DF1 link. See “Software Layers,” on page 1–7, for the layers your software driver must implement so that your intelligent device can talk to other DH, DH+, DH485, or ControlNet nodes.

Network Link
These network links are available for peer-to-peer communication: This link Connects And allows See page DH •PLC2, PLC3 processors •color graphic systems •personal computers •host computers •programmable RS232/RS422 devices up to 64 nodes➀ 1-3 DH+ •same devices as DH •PLC5 processors •SLC 5/04 processor up to 64 nodes 1-5 DH485 •SLC 500 processors •color graphic systems •personal computers up to 32 nodes 1-6 ControlNet •PLC5 processors •I/O devices •personal computers •operator interface devices up to 99 nodes –

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 PLC2 family DH PLC2 family communication adapter module (cat. nos. 1771KA2, KG) PLC3 DH PLC3 family communication adapter module (cat. nos. 1775KA,S5, SR5) PLC5/250 Resource manager module (cat. nos. 5130KA, RM1,RM2) PLC5, SLC 5/04➀ DH+/DH communication module (cat. no. 1785KA) ➀ Although a PLC5 processor does not directly connect to a DH link, it can communicate with devices on a DH link via the 1785KA 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

Unlike a master/slave relationship, a floating master relationship does not require the current master to poll each node to grant permission to transmit. Therefore, it provides a more efficient network because there is less overhead—i.e., time—per transaction.

DH+ Link A DH+ link is similar to a DH link, but is optimally used for smaller networks consisting of limited nodes (about 15 maximum). A DH+ link accepts 64 devices and can transmit data at 57.6, 115.2, or 230.4K bits. (PLC-5/250, SLC, and PLC processors support 57.6 and 115.2K bits; SLC 5/04 processors support 230.4K bits; PLC-5 processors are expected to support 230.4K bits early in 1997.) This processor Connects to a DH+ link PLC2 through the PLC2 Family Interface module (cat. no. 1785KA3) PLC3 through the I/O Scanner Communication Adapter module (cat. nos. 1775S5,SR5) PLC5 directly PLC5/250 through the Resource Manager module (cat. nos. 5130KA, RM1, RM2) SLC 5/04➀ directly ➀ You can configure the data rate for SLC 5/04 processors. A DH+ link implements peer-to-peer communication with a token-passing scheme to rotate link mastership among the nodes connected to that link.

DH485 Link A DH485 link is a low cost, peer-to-peer programming and data-acquisition link for a variety of Allen-Bradley products. DH485 topology is similar to DH and DH+ topology. You can connect as many as 32 nodes to a DH485 link. The DH485 link is based on the Electrical Industries Association (EIA) Standard RS-485 Electrical Signalling Specification. A variety of Allen-Bradley products (including SLC 500 controllers, 1784-KTX, 1747-KE, 1770-KF3, and operator interface devices) act as token-passing masters on the DH485 link. This link also supports a respond-only mode for low-level devices on the link, such as Allen-Bradley bar code decoders. A DH485 link implements peer-to-peer communication with a token-passing scheme to rotate link mastership among the nodes connected to that link.