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Protocol Configuration
Publication 1763-RM001C-EN-P - October 2009
Addressing Tips
Each station on the network, including the master station, must have a
unique address. The address range is 0 to 254, so you can have a
maximum of 255 stations on a single telemetry network. Station address
255 is the broadcast address, which you cannot select as a station's
individual address.
DF1 Half-Duplex Master Standard Polling Mode
With standard polling mode, the master device initiates all communication
by polling each slave address configured in the priority and normal
polling ranges. The slave device may only transmit message packets when
it is polled by the master. Based on a slave's inclusion in the priority and/
or normal poll ranges, the master polls each slave on a regular and
sequential basis to allow slave devices an opportunity to communicate.
During a polling sequence, the master polls a slave either repeatedly until
the slave indicates that it has no more message packets to transmit
("standard polling mode, multiple messages per scan") or just one time
per polling sequence ("standard polling mode, single message per scan"),
depending on how the master is configured.
The polling algorithm polls all of the priority slave addresses each poll
scan (priority low to priority high) and a subset of the normal slave
address range. The number of normal slave addresses to poll each poll
scan is determined by the Normal Poll Group Size configuration
parameter. In order to poll all of the slave addresses each poll scan with
equal priority, you may define the entire slave address range in either the
Priority Poll Range or the Normal Poll Range, and leave the other range
disabled. The Polling Range is disabled by defining the low address as
255.
An additional feature of the DF1 Half-Duplex protocol in Standard Polling
Mode operation is that it is possible for a slave device to enable a MSG
instruction in its ladder program to send or request data to/from the
master or another slave. When the initiating slave is polled, the message
command is sent to the master. If the message is addressed to the master,
then the master replies to the message. If the master recognizes that the
message is not intended for it, but for another slave, the master
immediately re-broadcasts the message so that it can be received by the
intended slave. This slave-to-slave transfer is a built-in function of the
master device and can also be used by programming software to upload
and download programs to processors on the DF1 Half-Duplex link.
Standard Mode Channel Configuration
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