Horner APG SmartStack I/O HE800DNS600/HEDNS600 - Manual (Page 27)

MAN0577-03-en
Page 27 of 98 EO 09-0009
DeviceNet Modules
HE800DNM650 & HE800DNS600
4.9
Actual chosen IO Connection
DeviceNet allows several kinds of I/O connections between devices. Please note that a device does not
have to support all types of IO connections.
I/O connection
Poll
Bit Strobe
Change of State
Cyclic
Table 6: Overview I/O Connections
The different connections types are :
• Polled I/O Connection - One poll command from the Master sends a number of output data to a
single, specific device (point-to-point). The device receives (consumes) the poll command and
processes the output data. If it has input data configured for this poll connection it reacts by sending
(producing) back a number of input data and/or status information to the Master. Before a polled I/O
connection is initiated by the Master, it reads the Consumed and Produced Connection Size of the
data from the Slave first and compares each value with the internally configured one. If the Master
detects differences the connection cannot be established. Sending a poll command can happen at
any time the Master wants to and has timer or event dependencies. A device has to respond if it has
consumed and understood the poll command request of the Master, even if it has no input data.
Otherwise the Master will report a timeout error. Polling data to many devices has the disadvantage
that the network traffic rate is very high and most data which is transferred has not changed since the
last transmission. Furthermore the higher the bus load more communication errors can occur if the
bus is disturbed by external influences.
• Bit Strobe I/O Connection - Bit strobe command and response messages rapidly move small
amounts of I/O data between the Master device and one/some/all Slave devices. The bit strobe
message contains a bit string of 64 bits of output data, one output bit per possible device. Each bit is
assigned to one device address in the network. This service has broadcast functionality that means
more than one Slave device can be addressed by one command. Because all addressed Slave
devices get this command at the same time, this command is normally used to synchronize data
transfer to several Slave devices. A Slave device can take its corresponding output bit as a real
output information to give it to the peripheral connections (e.g. an LED) and/or use the bit as a trigger
to send back its input data with a poll response message. The data that can be send back from each
Slave after a bit strobe command was received is limited to 8 bytes in length. Bit strobe connections
reduce the bus loading.
• Change of State/Cyclic I/O Connection - The Master device sends a number of output data to a
single, specific device (point-to-point). Data production is triggered by either a determined changed
value in the output data or the cyclic timer expiration. Depending on how the Slave behaviour is
configured, the Slave can send back an acknowledge message, containing a number of input data
and/or status information. The Slave device sends a number of input data to the Master, if the data is
either changed or the cyclic timer has expired. The Master itself can acknowledge this message with
output data if configured.
• Change of state only production of data hold down the bus load as small as possible, while data than
can be transmitted as fast as possible by each device because bus conflicts are less possible. High
performance data transmission can be achieved with comparatively low baud rates.