User manual

Chapter 4 Configuration
Page 73 ©February 2009
Modbus Retry Delay
The 105G Modbus Master configuration includes a feature to limit the frequency at which slave
devices are polled for data. The 105G will poll each Modbus slave in order. If there is no delay
time entered, the 105G will poll as quickly as it is able to. If there is a delay time entered, then this
delay time will occur between each poll message.
When updated values are received from the 105U radio network, the current polling sequence is
interrupted, and the new values are written immediately to the appropriate slaves.
Re-tries on the Serial Port
When communicating with Modbus slaves, the 105G may be configured to re-try (or re-send) a
message zero or more times if no response is received from a slave. If all retries are used up, that
slave is flagged as being in communication failure. Further attempts to communicate with the
slave will have zero re-tries. When a successful response is received from the Modbus slave, the
communication failure flag is reset and the configured number of re-tries will be used. This
means that an off-line slave device will not unduly slow down the communications network.
Comms Fail
“Comms Fail” image location in the 105G database. This image location should be in the range
4500 to 4999. If a response is not received from the Modbus slave after all re-tries have been
sent, the 105G will set this Comms Fail image location to hex (FFFF). When the 105G sends the
next poll for this I/O Command, it will not send any re-tries if a response is not received to the
first message. When a response is eventually received, the 105G will reset the value in Comms
Fail image location to 0, and the normal re-try sequence will operate.
Different I/O Commands can use different Comms Fail image locations; however we
recommend that you use the same image location for all I/O Commands to the same Modbus
slave address.
4.8 Serial Configuration - DF1
The 105G DF1 Driver allows the 105G to communicate with Allen-Bradley devices supporting
the DF1 protocol. Supported commands allow communication with 500 CPU devices (SLC and
Micrologix) and with PLC2 series devices. DF1 offers both full-duplex (point to point) and half-
duplex (multidrop) operation. The 105G only supports the full-duplex operation - this is the
default DF1 mode on most equipment. DF1 full-duplex is a “peer-to-peer” protocol. Either DF1
device can initiate commands to the other device, or both devices can respond to commands from
the other device. The 105G can act as both a command initiator and a command responder.
For more details please refer to the download section of the ELPRO Technologies website -
www.elprotech.com for an application note explaining how to configure an Allen-Bradley PLC
(Micrologix 1500) to a DF1 105G
The 105G will initiate the following command types to a command responder, according to the
configuration. The 105G will automatically generate the correct command type depending on the
configuration you enter. The 105G will also respond to these command types if they are sent
from a command initiator.