15.1.15
echolink one2PROFINET V. 1.0
20
Softing Industrial Automation GmbH
Implemented protocols in echolink one
8.3.3.4
Retries
In the event of negative acknowledgement or timeout, a telegram transmitted by the high-priority
user is repeated twice. After this, the gateway signals communication as disturbed but still
attempts to re-establish the connection.
8.3.3.5
Initiation of data communication by the high-priority user
In the case of a negative acknowledgement or timeout, a telegram transmitted by the external
device is repeated twice before a fault is signalled.
8.3.4
Protocol type 3964
The difference to protocol type 3964R is:
1. tq = acknowledge monitoring time
2. The checksum byte BCC is missing.
8.4 Protocol: MODBUS-RTU
8.4.1
Notes
For reasons of simplicity, "MODBUS-RTU“ is referred to as "MODBUS“ in the text below.
The terms "input“ and "output“ are always viewed from the gateway’s point of view,
i.e. fieldbus input data is the data sent by the fieldbus Master to the gateway.
8.4.2
echolink one as MODBUS-Master
8.4.2.1
Preparation
Before data exchange is commenced, the parameters "B
aud rate
", "
Parity
", "
Start bits
",
"
Stop bits
" and "
Data bits
" and, if applicable, the "
Trigger byte
" and the "
Length
byte
" must be set.
In addition, a "
Response time
" which corresponds to the maximum time up to which the Mod-
bus Slave responds after a request must be set. echolink one multiplies the value entered in
WINGATE by 10 ms.
Since the Modbus operates with a variable data format - dependent on the required function and
data length - but since the fieldbus requires a fixed data length, this must be preset by means of
a selection in the GSDML file (input and output are identical). This length should be selected by
the user such that the longest Modbus request resp. response can be processed.
The user can choose whether the fieldbus requests are forwarded to the Modbus in case of a
change (On Change) or on request (On Trigger).
In "
Change
" mode, detection of a change is based on the fact that the fieldbus data is compared
with that of the last transmission, and a request is issued by the Modbus only in the case of a
change.
The mode "
Modbus request on demand
" necessitates the first byte in the fieldbus containing
a trigger byte (see chapter 8.5). This byte is not transferred to the Modbus and serves only to
start a Modbus transmission. For this purpose, the gateway constantly monitors this trigger byte
and sends data to the Modbus only when this byte has changed. In the reverse direction (to the
fieldbus), the gateway transfers the number of received Modbus data records in this byte, i.e. this
byte is incremented by the gateway after each data record.
