Editing Profibus (section)

== Technology ==
{| border="0" cellspacing="3" style="margin:1em auto"
|+ '''PROFIBUS Protocol ([[OSI reference model]])'''
! colspan="2" | OSI-Layer
! colspan="3" align="center" | PROFIBUS
|-----
| align="center" bgcolor="#ffff99" | 7
| align="center" bgcolor="#ffff99" | Application
| align="center" bgcolor="#ffcc99" | DPV0
| align="center" bgcolor="#ffcc99" | DPV1
| align="center" bgcolor="#ffcc99" | DPV2
| rowspan="7" align="center" bgcolor="#cccccc" | Management
|-----
| align="center" bgcolor="#ffff99" | 6
| align="center" bgcolor="#ffff99" | Presentation
| colspan="3" rowspan="4" align="center" bgcolor="#dddddd" | --
|-----
| align="center" bgcolor="#ffff99" | 5
| align="center" bgcolor="#ffff99" | Session
|-----
| align="center" bgcolor="#ffff99" | 4
| align="center" bgcolor="#ffff99" | Transport
|-----
| align="center" bgcolor="#ffff99" | 3
| align="center" bgcolor="#ffff99" | Network
|-----
| align="center" bgcolor="#ffff99" | 2
| align="center" bgcolor="#ffff99" | Data Link
| colspan="3" align="center" bgcolor="#ffcc99" | FDL
|-----
| align="center" bgcolor="#ffff99" | 1
| align="center" bgcolor="#ffff99" | Physical
| align="center" bgcolor="#ffcc99" | [[EIA-485]]
| align="center" bgcolor="#ffcc99" | Optical
| align="center" bgcolor="#ffcc99" | MBP<!--It means Manchester Bus Powered.-->
|}

=== Application layer (OSI-Layer 7) ===
To use these functions, various service levels<ref name=iec61158-5-3/> of the DP protocol<ref name=iec61158-6-3/> were defined:<ref name=PI4072/><ref name=xiu4 />
* DP-V0 for cyclic exchange of data and diagnosis
* DP-V1 for acyclic data exchange and alarm handling<ref name=xiu2 />
* DP-V2 for [[isochronous]] mode and data exchange broadcast ([[master/slave (technology)|slave]]-to-slave communication)

=== Data link layer (OSI-Layer 2) ===
The data link layer '''FDL''' (Field bus Data Link) services<ref name=iec61158-3-3/>and protocols<ref name=iec61158-4-3/> work with a hybrid access method that combines [[token passing]] with a master/slave method. In a PROFIBUS DP network, the controllers or process control systems are the masters and the sensors and actuators are the slaves.<ref name=PI4072/><ref name=felser />

Each byte has even parity and is transferred asynchronously with a start and stop bit.
There may not be a pause between a stop bit and the following start bit when the bytes of a telegram are transmitted. The master signals the start of a new telegram with a SYN pause of at least 33 bits (logical "1" = bus idle).

Various telegram types are used. They can be differentiated by their start [[delimiter]] (SD):

==== No data ====
SD1 = 0x10
{| border="1"
|bgcolor="#ffff99"|SD1
|bgcolor="#ffcc99"|DA
|bgcolor="#ffcc99"|SA
|bgcolor="#77ffff"|FC
|bgcolor="#ff7777"|FCS
|bgcolor="#ffff99"|ED
|}

==== Variable length data ====
SD2 = 0x68
{| border="1"
|bgcolor="#ffff99"|SD2||LE||LEr||bgcolor="#ffff99" |SD2
|bgcolor="#ffcc99"|DA
|bgcolor="#ffcc99"|SA
|bgcolor="#77ffff"|FC
|bgcolor="#99ff99"|DSAP
|bgcolor="#99ff99"|SSAP
||PDU
|bgcolor="#ff7777"|FCS
|bgcolor="#ffff99"|ED
|}

==== Fixed length data ====
SD3 = 0xA2
{| border="1"
|bgcolor="#ffff99"|SD3
|bgcolor="#ffcc99"|DA
|bgcolor="#ffcc99"|SA
|bgcolor="#77ffff"|FC
||PDU
|bgcolor="#ff7777"|FCS
|bgcolor="#ffff99"|ED
|}

==== Token ====
SD4 = 0xDC
{| border="1"
|bgcolor="#ffff99"|SD4
|bgcolor="#ffcc99"|DA
|bgcolor="#ffcc99"|SA
|}

==== Fields ====
{| class="wikitable" border="1"
| '''SD'''
| Start Delimiter
|-
| '''LE'''
| Length of protocol data unit, (incl. DA, SA, FC, DSAP, SSAP)
|-
| '''LEr'''
| Repetition of length of protocol data unit, (Hamming distance = 4)
|-
| '''FC'''
| Function Code
|-
| '''DA'''
| Destination Address
|-
| '''SA'''
| Source Address
|-
| '''DSAP'''
| Destination [[Service Access Point]]
|-
| '''SSAP'''
| Source [[Service Access Point]]
|-
| '''PDU'''
| Protocol Data Unit (protocol data)
|-
| '''FCS'''
| [[Frame check sequence|Frame Checking Sequence]], calculated by simply adding up the bytes within the specified length. An overflow is ignored here.
|-
| '''ED'''
| End Delimiter (= 0x16)
|}

==== Service Access Points ====
{| class="wikitable" border="1"
! SAP (Decimal)
! SERVICE
|-
| Default 0
| Cyclical Data Exchange (Write_Read_Data)
|-
| 54
| Master-to-Master SAP (M-M Communication)
|-
| 55
| Change Station Address (Set_Slave_Add) – SAP55 is optional and may be disabled if the slave doesn't provide non-volatile storage memory for the station address.
|-
| 56
| Read Inputs (Rd_Inp)
|-
| 57
| Read Outputs (Rd_Outp)
|-
| 58
| Control Commands to a DP Slave (Global_Control)
|-
| 59
| Read Configuration Data (Get_Cfg)
|-
| 60
| Read Diagnostic Data (Slave_Diagnosis)
|-
| 61
| Send Parameterization Data (Set_Prm)
|-
| 62
| Check Configuration Data (Chk_Cfg)
|}

=== Bit-transmission layer (OSI-Layer 1) ===
Three different methods are specified for the bit-transmission layer:<ref name=iec61158-2/>
* With electrical transmission<ref name=PI8032/><ref name=xiu1 /> pursuant to [[EIA-485]], [[twisted pair]] cables with [[characteristic impedance|impedances]] of 150 [[ohm]]s are used in a [[bus topology]].<ref name=PI8022/> [[Bit rate]]s from 9.6 kbit/s to 12 Mbit/s can be used. The cable length between two [[repeater]]s is limited from 100 to 1200&nbsp;m, depending on the bit rate used. This transmission method is primarily used with PROFIBUS DP.
* With optical transmission via [[fiber optics]], [[star topology|star-]], [[bus topology|bus-]] and [[ring topology|ring-topologies]] are used. The distance between the repeaters can be up to 15&nbsp;km. The ring topology can also be executed redundantly.<ref name=felser />
* With MBP (Manchester Bus Powered) <ref name=xiu1 /> transmission technology, data and field bus power are fed through the same cable. The power can be reduced in such a way that use in explosion-hazardous environments is possible. The bus topology can be up to 1900&nbsp;m long and permits branching to field devices (max. 60&nbsp;m branches). The bit rate here is a fixed 31.25&nbsp;kbit/s. This technology was specially established for use in process automation for PROFIBUS PA.<ref name=felser />

For data transfer via sliding contacts for mobile devices or optical or radio data transmission in open spaces, products from various manufacturers can be obtained, however they do not conform to any standard.

'''PROFIBUS DP'''<ref name=mitchell /> uses two core screened cable with a violet sheath,<ref name=PI8032/> and runs at speeds between 9.6&nbsp;kbit/s and 12&nbsp;Mbit/s.<ref name=PI8022/> A particular speed can be chosen for a network to give enough time for communication with all the devices present in the network. If systems change slowly then lower communication speed is suitable, and if the systems change quickly then effective communication will happen through faster speed. The RS485 balanced transmission used in PROFIBUS DP only allows 31 devices to be connected at once; however, more devices (up to 126) can be connected or the network expanded with the use of hubs or repeaters (4 hubs or repeaters to reach 126).<ref name=PI8012/> A Hub or a Repeater is also counted as a device.<ref name=iec61784-5-3/>

'''PROFIBUS PA'''<ref name=powel /> runs at fixed speed of 31.25&nbsp;kbit/s via blue sheathed two core screened cable. The communication may be initiated to minimise the risk of explosion or for the systems that intrinsically need safe equipment. The message formats in PROFIBUS PA are identical to PROFIBUS DP.

Note: PROFIBUS DP and PROFIBUS PA should not be confused with [[PROFINET]].