The communications adapter consists of 4 hardware function blocks:
RS 485 PROFIBUS DP Interface
The communications adapter has a standard fieldbus interface for the PROFIBUS DP. The interface contains the PROFIBUS protocol chip and complies with the PROFIBUS DP standards per EN 50170 (DIN 19245 Parts 1 and 3 are integrated). The signals are executed as differential signals.
The ATI interface is an internal interface. It allows data exchange between the communications adapter and the I/O base.
The firmware for protocol execution is stored in an EPROM. The communications adapter’s firmware executes the protocols between the I/O module and the master. The transfer mode is half-duplex.
Integral functions are:
-
After voltage is applied or reset is activated, the communications adapter receives information about the data size requirement of the I/O base. The communications adapter also receives the I/O base group and code information. This information is provided by the I/O base.
-
The PROFIBUS DP master sends each slave (I/O module) the configuration data specified in the GSD file. Typical configuration data is e.g.: Identification of the I/O base, I/O data size etc. The I/O module compares the configuration data with its own actual data. If the data match, the master parameterizes the I/O module, and communication can be established.
-
If the I/O base detects an I/O error, the error signal is sent to the master as part of a (non-cyclic) diagnostic message (see evaluation of the,
I/O Error (Diagnostic Byte 8) diagnostic message).
The internal voltage supply (Vcc) is provided by the I/O base. Vcc is monitored and a reset signal is generated if and when Vcc is not within tolerance. The isolated voltage (Vcx) for the PROFIBUS DP interface is generated via a DC/DC converter and is not monitored.
Message Types and Data Transfer
The 170 DNT 110 00 PROFIBUS DP communications adapter recognizes three types of messages:
These messages are transferred in different cycles between the master and the I/O module (slave). The 170 DNT 110 00 communications adapter handles this task for the I/O module:
|
Transfer Cycle
|
Description
|
|
Cyclical transfer of the USER DATA
|
A transfer sequence in which input data is read from the DP slave by the master, and then output data is written to the DP slave. The parameters for analog modules are included in the I/O data.
|
|
Non-cyclic transfer of status information for diagnostics
|
If new diagnosis data is detected, a flag is set by the slave. This causes the master to poll the data.
|
|
One-time transfer of PROFIBUS DP internal parameters
|
Bus parameters, e.g. the ident number of the DP master that configures the slaves.
|
A serial microprocessor controls all of the operations within the 170 DNT 110 00
These include:
-
Sending a module error to the master via the PROFIBUS DP whenever an I/O base detects an I/O error.
-
The microprocessor controls a LED, which provides information about the data transfer (BF = Bus Fault), to provide a visual display of a network fault.
-
Setting the Data Control Time (DCT) for the DP master, which must take into consideration all the slave watchdog settings (e.g. if slave timeout is set for 250 ms, the DCT may be set to 1500 ms, a ratio of 6 to 1)
NOTE: The Data Control Time (DCT) and the watchdog times are entered with the corresponding bus projection tool during bus projection.
The master checks whether it had application data transmission with all slaves.
The watchdog time is set for each slave. If the slave hadn’t been polled by the master during this time, it sets its outputs to the defined shutdown value.
Additional information can be found in the software documentation for your PROFIBUS DP master.
