technical basics The PROFIBUS protocols Wiring Installation, DP- and PA-nodes Data representation on the bus Exchange of data, master / slave Cycle time, DP Mono-master-system Configuration GSD : Electronic data sheet Part 3 – PROFIBUS , Technical basics Page Subject The PROFIBUS protocols Wiring Pin assignement Termination, RS485 Installation, DP-nodes Installation, PA-nodes The smallest data package Data representation IEC – 6 1158-2 Stations, repeaters and segments Token ring Exchange of data, master/slave The 3 most common PROFIBUS telegrams Datatransmission at 1.5 MBaud Cycle time, DP Mono-master-system Configuration GSD-file (WINblock station) March 2003, Veslemøy Tyssø

The PROFIBUS protocols FMS DP PA User Layer (3)-(6) Application (7) Data Link (2) Physical (1) Application Profiles DP-Functions Fieldbus Message Specification (FMS) The principles for the FMS, DP and PA protocols are shown above. FMS and DP use the same transmission technology. The physical layer for these two protocols follow the standard EN 50 170. The PA standard for this layer is IEC 61158-2. The next layer, the link layer, is equally described in all three protocols. At user level, DP and PA are equal and FMS is different. not used IEC Interface* Fieldbus Data Link (FDL) RS-485 / Fiberoptikk IEC 61158-2 EN 50 170 DIN E 19245 partl 4 PROFIBUS guidelines March 2003, Veslemøy Tyssø

Wiring 2 wires shield The PROFIBUS-cable must have special characteristics conserning surge impedance, cable capacitance, core cross section, loop resistance and signal attenuation. It must be a twisted pair type cable with shield (braided and/or foil). A standard PROFIBUS cable has one green and one red wire. Red shall be connected to + or B and green to – or A at the PROFIBUS stations – see the next pages. March 2003, Veslemøy Tyssø

Pin assignement Standard 9 pin D-sub contacts are used with the pin assignments as shown above. Of the 9 pins only 4 are in use : 3 and 8 for signal + and - , 5 for grounding and 6 for power to the termination – se the next page. March 2003, Veslemøy Tyssø

Termination, RS485 Station 1 Station 2 Data line B Data line A Shield VP (6) Station 1 Station 2 390  Data line B RxD/TxD-P (3) DGND (5) VP (6) RxD/TxD-N (8) (3) RxD/TxD-P (5) DGND (6) VP (8) RxD/TxD-N RxD/TxD-P (3) 220  Data line A RxD/TxD-N (8) Shield The PROFIBUS cable must have a termination in each end of the bus. If this is not done, reflections will cause errors and the communication stops. The termination is done by connecting the two wires in the cable to a voltage as shown in the above picture. The resistance network lies usually inside the PROFIBUS contact and can be connected/disconnected to the VP and DGND by a switch on the contact. There are also some contacts that have no termination, and others with fixed termination. 390  DGND (5) March 2003, Veslemøy Tyssø

Installation, DP-nodes First station Last station Bus termination Bus termination VP VP 390  390  Data line B B B 220  220  Data line A A A 390  390  DGND A DP network should be wired as a bus with a termination in each end as shown above. The PROFIBUS cable goes typically from station to station. In the contacts on each station there are therefore always a double set of connection points A and B. DGND A B A B A B A B Station 2 Station 3 March 2003, Veslemøy Tyssø

Installation, PA-nodes Bus termination Bus termination Power Supply 100 100 1 F 1 F A PA network must have power supply. The mean value of the current is 10 mA – from which each PA station can be powered. There will be an upper limit of the number of stations per power supply – depending on power demands of the PA stations. The PA network must be terminated as shown above. …… Max 32 PA-stations March 2003, Veslemøy Tyssø

The smallest data package The OCTET 1. octet 2. octet Idle LSB MSB LSB PROFIBUS DP uses high and low voltage to represent each bit . When nothing is transmitted, the voltage is high. The 8 bits of data are packed in packages of 11 bits as shown above : The first bit is a low start bit, then comes the 8 data bits. The last bit is a high stop bit. After the data bits and before the stop bit, the package has a parity bit. This bit is set to 1 (high) or 0 (low) depending on the number of ones in the data word – and so that there always are an odd number of ones among the 11 bits of the package. The station that receives the package can then check for the number of ones and in that way check if errors have occured during transmission. So – already in the physical layer – there is an overhead of 3 bits for every 8 databits. The 11 bits that carries one byte (8 bits) are called an OCTET. The physical code used in DP and FMS, is called NRZ : Non Return to Zero Bit sequense: Start 1 2 3 4 5 6 7 8 Parity Stop Start March 2003, Veslemøy Tyssø

Data representation IEC – 6 1158-2 bit 2 1 bit 4 1 bit 6 1 I0+9mA I0 PROFIBUS PA uses another bit representation than PROFIBUS DP. The picture above shows how the data is modulated on top of the 10 mA current – giving a signal that changes between about 19 mA and 1 mA. Notice the bit representation which is called Manchester Code In this code it is always a shift for each data bit ( this differs from the NRZ code used in DP, see previous page). A shift from high to low means 1 and a shift from low to high means 0. I0-9mA bit 1 bit 3 bit 5 t March 2003, Veslemøy Tyssø

Stations, repeaters and segments Termination Termination Repeater Station 1 2 3 30 31 Termination Repeater Each PROFIBUS station is given a unique address which should be a number between 0 and 126. This means that it can never be more than 127 stations in a network. If the cables are long or the number of stations exceeds 32, it is a need for repeaters. Each segment has to be terminated in each end – see the picture above. 62 61 33 32 March 2003, Veslemøy Tyssø

Token ring PROFIBUS Logical token ring PLC PC PLC Aktive stations, MASTERS PLC PC PLC PROFIBUS PROFIBUS gives a deterministic network. This means that each station is guaranteed the access to the bus within a fixed time. This determinisme is taken care of by a token ring system – administrated from the data link level. The token passes between the masters . The station that holds the token can control the bus. The master communicates with all its slaves during the period it has the token. The master either sends data to the slave or asks the slave for data. A slave can not send any data without a request from its master. Passive stations , SLAVES March 2003, Veslemøy Tyssø

Exchange of data, master/slave DP-Slave Request Slave  Master DP-Master Data DP-Slave Data The above picture shows the principle of data exchange between master and slave. The master gets the data telegram from a slave after having sent a request telegram. When the master sends a data telegram to the slave, the slave must respond with a status telegram. Master  Slave DP-Master Status March 2003, Veslemøy Tyssø

The 3 most common PROFIBUS telegrams SDx = Start Delimiter x DA = Destination Address SA = Source Address FC = Function Code FCS = Frame Check Sequence ED = End Delimiter LE = Length LEr = Repeated Length DSAP = Destination Service Access Point SSAP = Source Service Access Point DU = Data Unit 1.) Token Passing SD4 DA SA 2.) FDL Status Request Telegram SD1 DA SA FC FCS ED In the picture above each little box is one OCTET – except for the DU, the Data Unit, which can be one or more octets depending on the length of data. The Token Passing telegram is three octets = 33 bits. The FDL Status Request telegram is 6 octets = 66 bits. The Data Telegram has a head of 9 octets = 99 bits and a tale of 2 octets = 22 bits. 3.) Data Telegram SD2 LE LEr SD2 DA SA FC DSAP SSAP DU FCS ED Head Tale March 2003, Veslemøy Tyssø

Data transmission at 1.5 MBaud Tbit = transmission time, 1 bit = 0.6667s OCTET : 11 Tbit = 7.3 s Token Passing : 33 Tbit = 22 s Status / Request : 66 Tbit = 44 s Data : Head (9 octets) + Tale (2 octets) + Data (n octets) 2 bytes of data : 13 x 11 Tbit = 143 Tbit = 95.3 s The example above shows how long time it takes to send 2 bytes of data, either from master to slave, or from slave to master. When calculating transmission times, it is common to use the term Tbit : 1 Tbit = the transmission time for 1 bit. 9.6 kBit/sek  1 Tbit = 0.1 ms 19.2 kBit/sek  1 Tbit = 0.05 ms . 12 Mbit/sek  1 Tbit = 0.08s In addition to the actual time for transmission, we must also calculate the time spent at the master side (Idle time for master) and at the slave side ( station delay time). In this way we can calculate the transmission time for all transmissions to/from all the slaves. Then we can calculate the total cycle time, taking into account an extra 10 to 20% for retransmitting and diagnostics. ” Idle time ” for master : typical 75 Tbit = 50 s ” Station delay time ” for slave : typical 11 Tbit = 7.3 s Total, 2 bytes of data : (33+66+143+75+11)Tbit = 0.219 ms March 2003, Veslemøy Tyssø

Cycle time, DP Mono-master-system Bus cycle time [ms] Each Slave : 2 bytes in / 2 bytes out 500 kBit/s 1.5 MBit/s In some installations it is important to decide an exact cycle time – which can be calculated as shown in the previous page. The cycle time will depend on the baudrate and the number of slaves, see picture above. 12 MBit/s Number of Slaves March 2003, Veslemøy Tyssø

PROFIBUS Configuration Software System Configuration Electronic Data Sheet (GSD - files) GSD PLC PLC The configuration of the PROFIBUS network is done in the software for the master. So – it looks a bit different for the Moeller PLC than for the Siemens PLC. But the principle is the same. Each PROFIBUS station must be accompanied by a GSD or GSE file which is an electronic data sheet. (GSD is German and stands for Geräte Stamme Datei). GSD-files can be downloaded from the PROFIBUS web site (www.profibus.com). The next three pages show the GSD-file for a WINblock station. The GSD-files must be installed in the hardware catalogue or data base of the configuration software. The network is configured by connecting to the PROFIBUS network the actual stations which must be present in the catalogue. Each station is referred to by its address. The baudrate, cycle time and other bus parameters are also set during configuration. The software gives default values of the bus parameters. PROFIBUS March 2003, Veslemøy Tyssø

GSD-file (WINblock station) ; WIWB0250.GSD ; Geraetestammdatei fuer PROFIBUS DP WINbloc 8 DI P ; Art.No. 827516 ; Weidmueller GmbH + Co, Postfach 2807, 33058Paderborn ; Serviceline 05252 960-555, Fax 05252 960116 ; Mailbox GSD, Siemens Typdateien: 05231 141555 ; Name:Gast kein Password ; ; Version: 1.6 Stand: 10.6.97 Km ;================================ ; #Profibus_DP GSD_Revision = 1 Vendor_Name = "Weidmueller Interface" Model_Name = "WINbloc 8DI" Revision = "V1.6" Ident_Number = 0x250

GSD-file cont. Protocol_Ident = 0 Station_Type = 0 FMS_supp = 0 Hardware_Release = "Ver.4" Software_Release = "00" ; 9.6_supp = 1 19.2_supp = 1 O.s.v 12M_supp = 1 MaxTsdr_9.6 = 60 MaxTsdr_19.2 = 60 MaxTsdr_12M = 800 Redundancy = 0 Repeater_Ctrl_Sig = 2 24V_Pins = 0 Implementation_Type = "LSPM2" Bitmap_Device = "winblocn" Bitmap_Diag = "winblocs" GSD-file cont.

GSD-file cont. ; Slavespezifische Werte ; OrderNumber = "827516" Periphery = "WINbloc" Freeze_Mode_supp = 1 Sync_Mode_supp = 1 Auto_Baud_supp = 1 Set_Slave_Add_supp = 0 Min_Slave_Intervall = 1 Modular_Station = 0 Modul_Offset = 0 Fail_Safe = 0 Slave_Family = 3@TdF@WINbloc Max_Diag_Data_Len = 13 User_Prm_Data_Len = 0x05 User_Prm_Data = 0x00,0x00,0x00,0x00,0x00 Module = "DP-Kompaktgeraet 8 I" 0x00,0x10 EndModule