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Siemens SIMATIC RK512 communication protocol

Supported device types and versions 
Communication line configuration
Communication station configuration
I/O tag configuration
Literature
Changes and modifications
Document revisions

Supported device types and versions


The protocol allows reading and writing data from control PLC automats of Siemens Simatic of the S5 and S7 series. PLC Simatic must be equipped with the following serial communication point-to-point modules:

  • SIMATIC S5 series: CP524, CP525 or CP544
  • SIMATIC S7-300 series: CP341
  • SIMATIC S7-400 series: CP441-2

The protocol RK512 is transport superstructure of the protocol 3964(R). It allows universal reading and writing values of PLC Simatic objects - minimal intervention into the PLC application software (using the STEPS5/7 programming language).

The 3964 protocol, that is the line layer of the RK512 protocol, has two variants - 3964 a 3964R. The 3964R allows extra data security using the BCC checksum.

Communication line configuration


Communication station configuration


  • Communication protocol: Siemens SIMATIC RK512.
  • There is not required any address parameter, one communication line allows to communicate with one PLC SIMATIC.


Station protocol parameters

The Communication station configuration dialog box - tab Protocol parameters.
Parameters defined in the input field have effect on some optional protocol parameters. The following station protocol parameters can be defined:

Table 1

ParameterMeaningUnit / sizeDefault value
Retry Count
Poll repetition count in case of a communication error.-2
Retry Timeout
Delay between poll repetition in case of a communication error.ms100 ms
Wait First Timeout
First waiting for response after sending the poll.ms100 ms
Wait Timeout
Delay between response readings till its finalization.ms50 ms
Max Wait Retry
Repetition count of response readings till its finalization.-40
3964 (without BCC)
Enable the 3964 link protocol, i.e. version with no transmission security. By default, there is used the 3964R protocol using the BCC checksum.YES/NONO
CPU id
CPU identification (1 up to 4), not used by default (value = 0).0,1,2,3,40

I/O tag configuration


Possible I/O tag value types: Ai, Ao, Ci, Co, Di, Do.

I/O tag address is a character string as follows:

  • the letter L denotes the left byte (higher) of the element
  • the letter R denotes the right byte of the (lower) element
  • the letter W denotes the interpretation of the element value as a 16-bit unsigned word (signed if KF suffix is used - see Note 1)
  • the letter D denotes the interpretation of values of 2 elements (address n and n + 1) as a 32-bit unsigned double word (signed if KF suffix is used, or float if suffix KG is used - see Note 1)
  • m - data block number is a number from interval 1..255
  • n - offset in data block as well as byte offsets are numbers from interval 0..255
  • k - bit position is a number from the interval 0..15 (for elements in Data block/Extended data block) resp. 0..7 (for Memory/Input/Output data)

Table 2

DataFormatDescriptionAccessI/O tag type
Data block/Extended data block elementsD{B|X}mD{L|R|W|D}n[x]m = "data block" number n = word offset in the data block x = suffix KF,KG (as necessary - see Note 1)R/WAi,Ao,Ci,Co
Data block bitsD{B|X}mDn.km = "data block" number n = word offset in the data block k = bit position [0..15]R/WDi,Do
Memory elementsF{Y|W|D}n[x] or M{B|W|D}n[x]n = byte offset in "memory area" x = suffix KF, KG (as necessary - see Note 1)RAi,Ci
Memory bitsFn.k or Mn.kn = byte offset in "memory area" k = bit position [0..7]RDi
Input elementsI{B|W|D}n[x] or E{B|W|D}n[x]n = byte offset in "input area" x = suffix KF, KG (as necessary - see Note 1)RAi,Ci
Input bitsIn.k or En.kn = byte offset in "input area" k = bit position [0..7]RDi
Output elementsQ{B|W|D}n[x] or A{B|W|D}n[x]n = byte offset in "output area" x = suffix KF, KG (as necessary - see Note 1)RAi,Ci
Output bitsQn.k or An.kn = byte offset v "output area" k = bit position [0..7]RDi

The table 2 contains the address format used in SIMATIC S5, i.e. use of word offset in DB and DX elements. Therefore you can use addresses in the S7 format according the table 3 for DB and DX elements:

Table 3

DataFormatDescriptionAccessI/O tag type
Data block/Extended data block elementsD{B|X}m.DB{B|W|D}n[x]m = "data block" number n = byte offset in data block x = suffix KF, KG (as necessary - see Note 1)R/WAi,Ao,Ci,Co
Data block bitsD{B|X}m.DBXn.km = "data block" number n = byte offset in data block k = bit position [0..7]R/WDi,Do

Explanatory text:

  • R/W = read and write
  • R = read only

Note 1:
Suffix is optional as follows:

  • KF - number (of word W type or dword D type) will be interpreted along with a sign.
  • KG - number will be interpreted as float (for dword D type) in the IEE754 format.

Literature


  • SIEMENS SIMATIC CP341 Point-to-Point Communication Installation and Parameter Assignment, Manual 6ES7 341-1AH00-8BA0

Changes and modifications


-

Document revisions


  • Ver. 1.0 - January 24th, 2002 - document creation.
  • Ver. 1.1 - November 3rd, 2010 - document update.
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