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SEMI E54.9-0303 © SEMI 2000, 2003 4 6.8 Application Layer — The device shall comply with the Modbus/TCP application layer specification for defining and addre ssing objects, including their attributes and services, an d …
SEMI E54.9-0303 © SEMI 2000, 2003 3
nection for simple field devices. The Modbus/TCP over
TCP/IP standard specifies OSI reference model layers
1, 2, 3, 4 and 7 specifically the physical signaling, the
media access/data link protocols, internetworking
capability, the transport capability of end-to-end
transmission of data, and the application layer.
5.4.4 peer-to-peer — on Modbus/TCP over TCP/IP
networks, messages formatted according to the
Modbus/TCP protocol are embedded into the TCP
packet structure that is used on the TCP/IP network.
The Modbus protocol over TCP/IP supports the
asynchronous or unsolicited bi-directional transmission
of data between nodes. This type of communication is
referred to as peer-to-peer.
6 Communication Protocol High Level
Structure
6.1 The Modbus/TCP protocol over TCP/IP is loosely
based on a five-layer architecture. These layers
constitute a collapsed form of the OSI seven layer
architecture, mapping into the physical, data link,
network, transport, and application layers of the
Reference Model. This section has been formatted to be
aligned with the Basic Reference Model for OSI. The
high-level protocol architecture is shown in Figure 1.
Application Layer Application Layer
Presentation Layer
Session Layer
Transport Layer Transport Layer
Network Layer Network Layer
Data Link Layer Data Link Layer
Physical Layer Physical Layer
Layered View of Modbus/TCP
OSI Reference Model
Figure 1
Layered View of Modbus/TCP Over TCP/IP
NOTE 2: Figure 1 represents a conceptual view of the com-
munication device architecture. Conforming implementations
must implement the services defined in this specification at
each layer and must appear (from the network) to have
implemented this architecture, however, an internal modular
partitioning is not required. Implementations may sacrifice
modularity in order to achieve high performance.
6.1.1 The application layer is specified in the Modicon
Modbus Protocol Reference Guide and provides for the
definition of Modbus applications as a collection of
addressable objects. A subset of these objects may be
addressed over the network (as defined by the
implementation).
6.1.2 In the remainder of this section the protocol
structure is described in more detail in terms of the OSI
seven layer reference model, the object model
environment and network management specifications.
6.2 Physical Layer — The device shall comply with a
physical layer specification identified in the
Modbus/TCP specification. The recommended and
default Modbus/TCP physical layer is IEEE 802.3. If
an accepted physical layer specification other than
IEEE 802.3 is being used, this must be clearly specified
in product literature. Physical layer specification
includes physical signaling (levels and data rates),
transceivers, node isolation, media topology, cable
specifications, network connectors and taps, and power
considerations (load limits, system tolerances, and
power supply options).
6.3 Data Link Layer — The device shall comply with a
data link layer specification of the Modbus/TCP
specification. The recommended and default Modbus/
TCP data link layer is IEEE 802.3. If an accepted data
link layer specification other than IEEE 802.3 is being
used, this must be clearly specified in product literature.
Data link layer specification includes the media access
control mechanism and the logical link control
mechanism.
6.4 Network Layer — The device shall comply with a
network layer specification of the Modbus/TCP specifi-
cation. This specification is the IP or Internet Protocol
as defined in the Modbus/TCP standard specification.
The network layer specification includes network
routing and internetworking.
6.5 Transport (Messaging) Layer — The device shall
comply with the Modbus/TCP standard specification
for the Transport Layer. This specification is the
Transmission Control Protocol as defined in the
Modbus/TCP standard specification. The transport
layer provides transparent transfer of data between
objects in application-entities. Some of the functionality
of this layer is implemented in the Application Layer.
Specific functions include: object data segmentation/re-
assembly (fragmentation) for full message delivery.
6.6 Session Layer — There is no distinct session layer.
6.7 Presentation Layer — There is no distinct
presentation layer. Object addressing and data
presentation in Modbus messages are specified as part
of the Modbus object definitions and object attribute
and service communication protocol. Data byte
transmission ordering is defined in IP RFC 791,
Appendix B.
SEMI E54.9-0303 © SEMI 2000, 2003 4
6.8 Application Layer — The device shall comply with
the Modbus/TCP application layer specification for
defining and addressing objects, including their
attributes and services, and enabling specified network
behavior. The device shall comply with the object
messaging and object model specifications included in
the Modbus/TCP standard specifications. In addition,
the device shall comply with the object specifications
defined in Section 7 of this document.
6.8.1 Object Models — The Modbus/TCP protocol has
been enhanced to provide an object-oriented specifica-
tion for creating, defining, and addressing objects
explicitly, including their attributes and services, and
creating, defining, and communicating object attributes
in an application dependent format. The device shall
comply with the object messaging and object model
specifications included in the Modbus/TCP standard
specification documentation. In addition, the device
shall comply with the object specifications defined in
Section 7 of this document.
6.9 Network Management — The device shall comply
with the Modbus/TCP and TCP/IP network manage-
ment specifications detailed in the Modbus/TCP Stan-
dard Specifications (e.g., physical layer bit rate, master/
slave and peer-to-peer network management, etc.). No
(additional) network management functions are
specified in this document.
7 Required and Optional Object Types
7.1 At this time, the Modbus/TCP standard specifica-
tions do not require any specific objects to exist in a
Modbus/TCP device in order to be a compliant Mod-
bus/TCP device. The Modbus/TCP standard specifica-
tions will be extended to identify and describe objects
(i.e., classes) that must exist in devices that are to be
interoperable and interchangeable on a Modbus/TCP
SEMI compliant SAN network.
7.1.1 The Common Device Model (CDM) specifica-
tion identifies two objects (namely the Device Manager
(DM) and Sensor Actuator Controller (SAC) objects)
that must exist in all SEMI compliant SAN devices.
7.1.2 The required object types for a SEMI compliant
SAN device utilizing the network communication
specification described herein, necessarily comprises, at
minimum, the union of the Modbus/TCP object type
requirements and the CDM specification requirements.
7.1.3 A list of required and optional object types is
given in Table 2. Additional objects that are specified
in a particular SDM are given identifiers in that SDM
specification. Modbus specific presentation information
for these identifiers is given in Section 9 of this
document.
Table 2 Required and Optional Object Types
Object Name Modbus Class
ID/Instance ID
(See Note 1)
CDM Tag
(See Note 2)
Required by
Modbus
(See Note 1)
Required by
CDM
(See Note 2)
Required by
NCS
Device Manager 1/1 DmI0 No Yes Yes
Sensor/Actuator/
Controller
2/1 SacI0 No Yes Yes
Assembly 3/1 through i Asm No No No
Local Link 4/1 through j Lnk No No No
Sensor – AI 33/1 through k Sai No No No
Sensor – EI 34/1 through l Sei No No No
Sensor – BI 35/1 through m Sbi No No No
Actuator – AO 36/1 through n Aao No No No
Actuator – EO 37/1 through o Aeo No No No
Actuator – BO 38/1 through p Abo No No No
Controller 39/1 through q Ca No No No
Application Objects 129 through x/
1 through r
(See Note 3) No No No
NOTE 1: See Modbus specification for further information; values are decimal: “i”, “j”, “k”, “l”, “m”, “n”, “o”, “p”, “q” and “r” represent
arbitrary numbers (greater than or equal to 1) indicating that more than one instance may be supported. “x” is a number greater than or equal to
129 indicating that one or more application object classes may be supported.
NOTE 2: See CDM specification for further information.
NOTE 3: Application Dependent objects as specified in SDM.
SEMI E54.9-0303 © SEMI 2000, 2003 5
7.1.4 An embodiment of a specific device type
represented as an aggregation of the object types listed
in Table 2 that is compliant with both the CDM
specification and the Modbus/TCP specification, is a
candidate for a SEMI SDM as well as a Modbus/TCP
device definition. Conversely, all SEMI SDM’s and
Modbus/TCP device definitions specified for operation
over a SEMI compliant Modbus/TCP network must be
an aggregation of the object types listed in Table 2, and
be compliant with both the CDM specification and the
Modbus/TCP standard specifications.
7.1.5 In the following sections the presentation to the
network of object addressing, object attributes, and
object services for each of the object types listed in
Table 2 is described in detail. Refer to the CDM
standard to determine if the object instance attribute and
service is specified as required or optional. Unless
otherwise noted, all attributes and services described
are instance level attributes (as opposed to class level
attributes). A class level attribute and service is
accessed as instance number zero.
NOTE 3: The formats of object attributes and services are
detailed in the CDM document; the presentation of object
attributes and services to the Modbus/TCP over a TCP/IP
network is detailed in the tables contained in the following
sub-sections and in the Modbus/TCP standard specifications.
7.2 Device Manager (DM) Object
The DM object
instance is the device component responsible for
managing and consolidating the device operation. Each
device must support one (and only one) DM object.
The DM object as well as its common required and
optional attributes, services and behavior are described
in the CDM standard. The presentation of object
instance attributes and services to the Modbus/TCP
network shall be as indicated in Table 3. Note that all
service ID values identified refer to the ID of the
request or notification component of that service.
Corresponding reply components to request/reply
services shall have a service ID value equal to the
request component ID plus one.
Table 3 DM Object Instance Attributes and Services
Device Manager Object (DM)
Class ID = 01, Instance ID = 01
Attributes
ID Attribute Name CDM Tag
01 Device Type DmA1
02 Standard Revision Level DmA2
03 Device Manufacturer Identifier DmA3
04 Manufacturer Model Number DmA4
05 Software or Firmware Revision
Level
DmA5
06 Hardware Revision Level DmA6
Device Manager Object (DM)
Class ID = 01, Instance ID = 01
07 Serial Number DmA7
08 Device Configuration DmA8
09 Device Status DmA9
12 Exception Status DmA12
13 Exception Detail Alarm DmA13
14 Exception Detail Warning DmA14
15 Visual Indicator DmA15
16 Alarm Enable DmA16
17 Warning Enable DmA17
18 Exception Detail Type DmA18
19 Exception Detail Alarm Queue DmA19
20 Exception Detail Warning Queue DmA20
Services
ID Service Name CDM Tag
01 Reset DmS1
03 Abort DmS2
05 Recover DmS3
07 Get Attribute DmS4
09 Set Attribute DmS5
11 Execute DmS6
13 Perform Diagnostics DmS7
15 Publish Attribute DmS8
17 Lock DmS9
19 Unlock DmS10
21 Get Exception Queue DmS11
23 Clear Exception Queue DmS12
7.3 Sensor, Actuator, Controller (SAC) Object –– The
SAC object instance is the device component respons-
ible for coordinating the interaction of the device with
the sensory/actuation/control environment. Each device
must support one (and only one) SAC object instance.
The SAC object instance as well as its common
required and optional attributes, services, and behavior
are described in the CDM standard. The presentation of
object instance attributes and services to the
Modbus/TCP network shall be as indicated in Table 4.
Table 4 SAC Object Instance Attributes and
Services
Sensor, Actuator, Controller Object (SAC)
Class ID = 02, Instance ID = 01
Attributes
ID Attribute Name CDM Tag
01 Last Calibration Date SacA1
02 Next Calibration Date SacA2
03 Expiration Timer SacA3
04 Expiration Warning Enable SacA4