The s7nodave device support is based on Snap7. This library implements the communication protocol supported by many PLCs from the S7 family and thus allows software on a PC to communicate with a PLC without having to explicitly implement communication routines on the PLC side.

In the past, the s7nodave device support had been based on libnodave. This changed with the release of s7nodave version 3.0 because of a bug in libnodave that could not be easily fixed.

Basically, s7nodave supports all PLCs supported by Snap7.

S7nodave has been developed using a S7-1200 PLC. However, we have also seen it work with S7-300 and S7-1500 PLCs.

For new version of PLCs or TIA Portal, (in particular S7-1200 and S7-1500 series PLCs and TIA Portal version 12 and newer) the settings in the S7 project might have to be changed in order to allow full access to the PLCs memory. You might only be able to access global DBs and optimized block access for those DBs must be disabled. In addition to that, the access level must be set to full and the connection mechanism must allow GET/PUT communication. Please refer to the information available from the Snap7 project for a more detailed guide, including screenshots of the relevant configuration dialogs.

The S7plc driver from PSI is based on a whole data-block being exchanged between the PLC and the EPICS IOC. This means, that it is not possible to write single records to the PLC. Instead, all values must be sent at once. The same applies to read requests. Besides, the structure of the data-block is coded into a PLC program. If a value is added or removed from the block, the addresses in the PLC logic as well as in the EPICS record configuration have to be updated.

The s7nodave device support on the other hand, directly reads from and writes to memory addresses in the PLC. The addresses configured in the EPICS records use the same notation that is used for programming the PLC logic. When an output record is process, on the value of this record is sent to the PLC. For input records, different records can be processed at different rates and only the values in the same poll group are transferred together.

S7nodave is implemented as an asynchronous device support based on asynDriver. While the asynDriver is used for configuration management, logging and asynchronous processing, neither the device support nor the low-level I/O routines supported by the asynDriver are used.

S7nodave has three prerequisites: First, EPICS base R3.14.12 or higher is needed. Older versions of EPICS base might work but in this case support for the aai and aao record types must be disabled, because these record types were broken in earlier versions of EPICS base.

In addition to that, the asynDriver is needed. S7nodave has been developed against version 4.13 of asyn, however most likely it also works with newer versions.

A minimal version of Snap7 that contains all the parts needed by s7nodave is bundled with s7nodave and automatically compiled when s7nodave is compiled. Thus, you do not need to download or compile Snap7 yourself.

S7nodave has been developed under Linux, but should work on most POSIX-compliant operating systems. On Microsoft Windows, you will have to use a compatibility layer like Cygwin or change the network code in s7nodave to use the respective functions from the Windows API.

For compiling EPICS Base and the asynDriver, refer to the respective manuals.

After downloading s7nodave from the project website, extract it to the directory you want it to install in. A good place might be the /opt/epics/modules directory.

Subsequently, you have edit add the file configure/RELEASE.local in order to configure the locations where EPICS base and the asynDriver are installed. Add the variables ASYN and EPICS_BASE to this file and make them point to the right directories. You can find an example in configure/EXAMPLE_RELEASE.local.

S7nodave must be compiled with a C++ compiler that supports C++ 11. For some compilers, C++ 11 support is not enabled by default. In this case, you have to add the file configure/CONFIG_SITE.local and append the appropriate compiler options to the USR_CXXFLAGS variable. An example for such a configuration file can be found in configure/EXAMPLE_CONFIG_SITE.local.

After editing this paths, you can run make to build s7nodave.

In the configure/RELEASE file of your project, you have to add a line like S/NODAVE=/opt/epics/modules/s7nodave. In the Makefile of the src directory of you application (e.g. myApp/src/Makefile) you have to add something like

my_DBD += s7nodave.dbd
my_LIBS += s7nodave

in order to use the s7nodave device support in your record definition files.

Finally, you have to configure at least one PLC connection in the startup file of your IOC. See Section 4.1, “s7nodaveConfigureIsoTcpPort” for the syntax of the corresponding command. Optionally, you also might want to configure poll groups. For defining records that read from or write to the PLC, please refer to the record reference.

The s7nodaveConfigureIsoTcpPort command is used to setup a connection to a PLC and command has the following syntax:

s7nodaveConfigureIsoTcpPort(PLC name, PLC hostname or IP address, PLC rack number, PLC slot number, thread priority)

The PLC name is an arbitrary string, that is used to refer to this PLC in the device address field of records and when configuring poll groups for the PLC. However, the PLC name may not contain whitespace or parentheses.

The PLC hostname or IP address is the DNS hostname or IP address of the PLC, optionally followed by the TCP port number (separated from the hostname or IP address by a colon). If no port number is specified, the default port (102) is used.

The PLC rack number and PLC slot number depend on the actual PLC configuration. For most setups, both numbers are zero, but rack 0, slot 2 might have to be used with some S7-300 series PLCs. If you cannot get access to the PLC, try to change those numbers. In case of doubt, you should be able to find the correct numbers in the configuration of your S7 project. You can find more information about rack and slot numbers in the reference manual of the Snap7 library.

The thread priority is the priority used for the communication thread (port thread in asyn nomenclature). If a priority of 0 is specified, the priority epicsThreadPriorityMedium is used.

An example line configuring a connection to a PLC might look like this:

s7nodaveConfigureIsoTcpPort("myPLC", "myplc.example.com", 0, 0, 0)

You can have multiple instances of s7nodaveConfigureIsoTcpPort in your IOC startup configuration, however the PLC name used must be unique for each instance.

The s7nodaveConfigurePollGroup command is used for configuring poll groups and has the following syntax:

s7nodaveConfigurePollGroup(PLC name, poll-group name, poll interval, thread priority)

The PLC name must be the name of a PLC previously used in an instance of s7nodaveConfigureIsoTcpPort.

The poll-group name is an arbitrary string that identifies the poll-group and must be unique for the PLC. However, the same poll-group name may be used for two different PLCs. The poll-group name must no contain whitespace, parentheses, the equal sign or commas.

The poll interval is a floating point number that specifies the interval in which the memory addresses belonging to the poll group are read. The units of the poll interval are seconds.

The thread priority specifies the priority of the thread, that periodically processes the poll group. If a priority of 0 is specified, the priority epicsThreadPriorityMedium is used.

An example line configuring a poll group that is processed once a second might look like this:

s7nodaveConfigurePollGroup("myPLC", "1s", 1.0, 0)

You can have multiple instances of s7nodaveConfigurePollGroup per PLC, however the poll-group name used must be unique for each instance referring to the same PLC.

In order to use the s7nodave device address support for a record, the record's device type field (DTYP) has to specify s7nodave. This device type is used for all records supported by s7nodave except the waveform record.

The record's device address field (usually INP for input and OUT for output records) must specify a device address recognized by the s7nodave.

In general, a device address for s7nodave has the following format:

@PLC-name[(param1=value1,param2=value2,...)] PLC-address [PLC-data-type]

The exact supported options may vary depending on the record type.

Every device address start with the @-sign, followed by the PLC name. The PLC name must be the name of a PLC configured using the s7nodaveConfigureIsoTcpPort statement in the IOC startup file.

The PLC name is followed by list of optional parameters wrapped in parentheses. If no parameters are given, the parentheses can be ommitted. The supported parameters depend on the record type. Please see Section 5.4, “Supported Parameters” and Section 5.5, “Supported Records” for details. If multiple parameters are specified, they are separated by commas.

The PLC memory address is separated from the PLC name (or the optional parameter list) by whitespace. Please refer to Section 5.2, “PLC Memory Addresses” for the the format of the PLC memory address.

Finally, an optional PLC data-type, which is separated from the PLC memory address by whitespace, can be specified. If no PLC data-type is specified, the data-type is guessed based on the record-type and PLC memory address. Please refer to Section 5.3, “PLC Data-Types” and Section 5.4, “Supported Parameters” for details about the supported PLC data-types.

Examples for valid device addresses:

S7nodave uses the same format for PLC memory addresses, that is also usually used for programming the PLCs (e.g. using Step7 or WinPLC). The English and the German notation are both supported and equivalent to each other.

This format combines the specification of the start-byte of a variable in the PLC memory with specification of the variable's width.

The PLC address starts with the memory area. The following memory areas are supported:

For data block addresses the data-block number has to be included in the area specification. For addresses using the data-block, flags, input-memory and output memory areas, you next have to specify the width of the memory that should be read from or written to. The notation used for specifying the width is:

For addresses referring to a single bit (with the exception of bit addresses in DB areas) and for addresses referring to the counter or timer areas, no width specification is given: Bit addresses are identified by specifying the bit within the byte and the counter and timer areas always use word (16-bit) values.

After specifying the memory width, the start address must be specified. The start address is always given in the number of bytes counted from the beginning of the respective area (starting with zero). For example, if at the beginning of DB1 two 32-bit numbers were stored, the two addresses for these numbers would be DB1.DBD0 and DB1.DBD4.

For addresses referring to a single bit, the start bit within the byte has to be specified, separated from the start byte by a dot. For example, in order to refer to the first bit of the first byte in the input-memory area, you would use the address I0.0. You must not specify a start bit for byte, word or double-word addresses.

PLC memory-address specifications are not case-sensitive. However, for enhanced readability the use of upper case characters is recommended.

Examples for valid memory addresses:

s7nodave supports eight different PLC data-types. Each of these data-types may only be used together with a memory address having the right width:

The available data-types are also limited by the used record-type. Please refer to Section 5.5, “Supported Records” for details.

There is a number of optional parameters that can be used to specify device-support specific options for a record. Most of these options are only valid for a specific record-type, so please refer to the description of the respective options for finding out which option can be used with which record type.

S7nodave supports most records from EPICS base, that have an interface for device support routines. In order to use s7nodave with a record, the record's DTYP and INP or OUT fields have to be set correctly. Please refer to Section 5.1, “Device Address Format” for details. This chapter describe the specific options for each supported record type.

This manual only describe those features of each record, which are specific to the s7nodave device support. Please refer to the EPICS Record Reference Manual for a general description of each record type and its fields.

A poll group is created using the s7nodaveConfigurePollGroup command in the IOC's statup configuration. If you use the poll-group name “default”, this has a special meaning. This poll-group is used for all records, that are configured to use a poll group but do not explicitly specify the name of the poll group to use. For each PLC that is configured, the default poll-group must be configured separately.

In order to make a record be processed in a poll group, the SCAN field of the record has to be set to I/O Intr. If you want to use a different poll group than the default poll-group, you can use the PG parameter to specify the poll group to use (see Section 5.4.1, “PG - Specifying a Poll Group”).