E 24
LOREME
12, rue des Potiers d'Etain - 57071 Metz
03.87.76.32.51 - Email: [email protected] - [email protected]
1) Data format:
1.1) Overview
The device is divided in two cells. Each cell has a specific function while keeping a continuous exchange of pieces of
information with the second cell. The first cell is in charge of the measure, analysis and conversion function? The sec-
ond cell is in charge of the communication function. The information exchange is continuous and automatic
1.2) Measure function
The measure cell run the acquisition of the different signals and calculates all values regards to the configuration of de-
vice. It also runs all the output functions (analogical, alarm, meter, RS232). All measures or calculated parameters are
stored in the system memory and are constantly refreshed.
1.3) Communication
The communication cell runs the RS485 communication interface in the PROFIBUS protocol. It analyzes the requests of
the master station and answer if the device is addressed. It draws all these data from the system memory that can be
continuously accessible.
1.4) System memory
Each cells can continuously access the system memory. The latter has a dual access, which allows a reading / writing of
the data without any possible internal conflicts.
2) Protocol overview
2.1) generality
PROFIBUS-DP use the scanning principle for master/slaves communication. It means that a slave station need requests
coming from a master for information exchange. Messages transfer is organized by cycles. A message cycle is made of
request frame send by active station (master) and an answer frame send back by a passive station (slave). Global con-
trol function exists and permit coordination and synchronisation of many slaves. Before a DP system be operational,
each station presents have to own a different address. For slaves, it can be directly made by a function throughout the
bus .
All slaves without definitive address start up with the 126 default address. It must be only one device possessing this
address. Only a supervisor can access to a slave via this address for fixing a specific address. For security, data ex-
change between a master and a "126" address slave is forbidden. For data exchange, master must have a valid data
base. This database include configuration and parametrical data necessary to each one of his slave. It can contain dif-
ferent bus parameters. If a base is present in a master, it begin by verification assigned slave presence or absence. For
present device, master process to the configuration parameterization and verification of each one of them. A slave will
accept the parameterization verification requests only if it come from the master which send the data parameters. When
these two operations are correctly made, master will inspect slave state by reading diagnosis data.
When ok, EXCHANGE DATA will be authorized.
A slave will accept an exchange request only if it come from the master who have configurated it. A master can send a
slave new parameters without leaving exchange data mode. Supervisors can read any slaves diagnosis, input and out-
put data. If an event appends in a slave process, it will signal by sending an high priority answer. If the master want to
know the event causes, it will have to read slave diagnosis data.
A supervisor can take the slave control every time. In case, slave stop data exchange with master. It recognize this
event and regularly verify the slave state until it be free. Master will take slave control by sending parametrical and con-
figuration data.
RS485 Profibus
