Profibus encompasses several Industrial Bus Protocol Specifications, including Profibus-DP, Profibus-PA, Profibus-FMS, and PROFInet.

Profibus-DP is a device level bus that supports both analog and discrete signals. Profibus-DP has widespread usage for such items as remote I/O systems, motor control centers, and variable speed drives. Profibus-DP communicates at speeds from 9.6 Kbps to 12 Mbps over distances from 100 to 1,200 meters. Profibus-DP doesn’t natively support Intrinsically Safe installations.

Profibus-PA is a full-function fieldbus that is generally used for process level instrumentation. Profibus-PA communicates at 31.25 Kbps and has a maximum distance of 1,900 meters per segment. Profibus-PA is designed to support Intrinsically Safe applications.

Profibus-FMS is a control bus generally used for communications between DCS and PLC systems, while PROFInet is a protocol being developed to allow Profibus communications across Ethernet Networks.

Profibus Network Highlights

Type of Network
DP	Device Bus
PA	Process Control Network
FMS	Control (cell level) Network
Physical Media	Twisted pair, fiber
Network Topology	Bus, Ring, Star
Maximum Devices
DP	max. 126 stations on one bus (maximum of 244 bytes input and output data possible for each slave)
PA	32 nodes/segment 4-6 per repeated segment depending on power requirements of devices and the type of I.S. barrier used.
Maximum Distance
DP	93.75Kbps and less – 1200 meters 500Kbps – 400 meters 1.5Mbps – 200 meters 12Mbps – 100 meters
PA	1,900 meters
Max Distance with repeater (max. of 9 repeaters can be used)	9,500 meters with repeaters
Communication Methods
DP	Peer-to-peer, multicast or cyclic master-slave (uses token passing sequence)
PA	Client/server, Publisher/subscriber, Event. Both Scheduled and Unscheduled communications
Primary usage
DP	Used for Discrete and Analog for PLC, Variable Speed Drives, Remote I/O communications
PA	Analog and discrete process control devices
Power and Communications
DP	Power is supplied separately from communications bus (can be supplied on a parallel power bus)
PA	Requires PA power supply (conditioner) to protect the digital communications
Device Power Supply
DP	Devices are powered separately from communications bus
PA	Can be supplied from bus (typical)
Wiring Types
DP	Shielded twisted pair #22 AWG
PA	Shielded twisted pair #18AWG (0.8mm) 1900m (6232 ft.)
Device Addressing	DIP switch settings or handheld/software
Governing Body	PROFIBUS International (PI)
Web Site	www.profibus.com

Conventional I/O System	Profibus DP-PA-FMS Networks
Advantages	Advantages
Technology is already understood	Widely accepted, with 1,100 member companies worldwide.
Lower device cost	Network support at the device, process control, and Ethernet levels
Independent wiring from devices to the control system means wiring problems with one device don’t affect other field devices	Interfaces are available for variable speed drive and motor control center applications (Profibus-DP)
Drawbacks	Process instrumentation available with Profibus-PA devices
Higher installed cost	Enterprise-wide applications with PROFInet
Point-to-point wiring is expensive	Intrinsically Safe installations available for Profibus-PA instruments
Many wiring connections: - - are labor intensive to install - - create many points of failure - - increase complexity when troubleshooting - - require large amounts of cabinet or rack space for installation of terminal blocks - - create time-consuming initial checkout and startup	Gateways allow for Profibus-PA integration directly to Profibus-DP networks
Expansion requires duplicating the entire wiring scheme for each additional point	Host interfaces available for most PLC, DCS and computer systems
	Gateway devices available to directly support lower cost Sensor Bus networks, especially AS-Interface
	More than 2,000 available products
	Drawbacks
	Profibus-DP does not support Intrinsically Safe installations
	No control in the field capabilities
	Segment wiring, power, grounding, shielding and termination requirements must be adhered to in the design and installation
Profibus-DP Network
Advantages	Drawbacks
Based on RS-485 physical layer	Not available for Intrinsically Safe installations
Multiple bus transmission speeds and wiring length combinations: - - Up tp 1000 m distance at 9.6kbits/sec, expandable to 2000 m using repeaters - - Up to 200 m at maximum speed of 1500kbits/sec.	Slaves not powered by network wiring, require separate power source
Supports both discrete and analog signals	Addressing set manually (not dynamic) Profibus-DP is recommended
I/O modules allow connection of conventional analog and discrete devices	For time critical analog and discrete applications due to its high speed capabilities
Interfaces available for many variable speed drives, motor control centers, and field devices	Where variable frequency drives and motor control centers can incorporate bus technologies
Supports 32 devices per segment, 62 with repeaters	For a mixture of conventional analog and discrete devices
Supports mono-master and multi-master systems
Simple integration of new devices to an existing system