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6. Configuring the Gateway
Configuration
element
Description
Retries This element indicates the number of re-transmissions carried out by the gateway if there is
no response from the Modbus slave to a query, or if the response is incorrect. This re-
transmission process ceases as soon as the gateway gets a correct response within a given
time. If none of the re-transmissions has allowed the gateway to obtain a correct response,
the Modbus slave is deemed to be off-line, but only in relation to the command in question.
The gateway then uses the “Offline options for sub-network” and “Reconnect time (10ms)”
elements and the LED
r MODBUS becomes red. This LED will only revert to a green state
if the Modbus command is answered with a correct response, once the reconnection has
started (see element “Reconnect time (10ms)”).
If the number of re-transmissions is set to 0, the process described above will not be run.
Timeout time
(10ms)
This element represents the time that the Modbus slave will wait for a response. If a
response has not reached the gateway within the given time, configured using the “timeout
time (10ms)” element, the gateway proceeds to a re-transmission. This process continues
until it reaches the last re-transmission allowed (see “Retries”), then the gateway declares
the Modbus slave off-line, but only for the command to which the “timeout time (10ms)”
belongs to.
Trigger byte
address
This element is only used by the gateway if “Update mode” is set to “Change of state on
trigger”. In this case, it specifies the address, in the gateway’s output memory (16#0202 to
16#02F3), of an 8-bit counter managed by the Profibus-DP master.
When the value located at this address is changed by the Profibus-DP master but
different
from zero, the query configured with a “Change of state on trigger” related to this address is
transmitted to the Modbus slave. So the Profibus-DP master must have access to this
counter in the same way as for the periodic output registers sent to TeSys U motor starters.
In comparison to the “On data change” mode, this mode allows you to send a command on
a specific order from the Profibus-DP master if, for example, the latter is unable to update
all data from of any given query at the same time.
N.B. In the specific case of the gateway’s default configuration, the “Transactions 1” and
“Transactions 2” personalized command mode for the “TeSys U n°1” node is set to “Change
of state on trigger”. These aperiodic commands are respectively used to read and write the
value of a parameter of one of the Modbus slaves.
The “Trigger byte address” elements of the “Query” elements of these two commands are
configured at addresses 16#021E and 16#021F. These are the “parameter read/write
request counters”. Considered under Profibus-DP, SyCon, and PL7 PRO, these two data
are configured the same way as the other outputs (see chapter 4.2.9 Configuring the
Gateway I/O under PL7 PRO, page 32) and both correspond to the %QW4.0.15 output.
To transmit one of these two commands, the Profibus-DP master PLC must first of all
update all of the data to be transmitted on the Modbus network for this command
(addresses 16#0212 to 16#0217 or addresses 16#0218 to 16#021D), then change the
value of the associated counter (address 16#021E or 16#021F). The gateway will then
transmit the query corresponding to the command.
N.B. The “trigger byte” does not have to be an item of output data updated by the Profibus-
DP master. In fact it is quite possible that it may be an input between 16#0002 and
16#00F3. In this case, the Modbus slave which updates this byte will condition the
exchanges of the command you’re currently configuring.