17.7.17
UNIGATE
®
fieldbus gateway UNIGATE
®
MB - EtherCAT
®
V. 1.4
21
Deutschmann Automation GmbH & Co. KG
Implemented protocols in UNIGATE® MB
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
UNIGATE
®
as MODBUS-Master
8.4.2.1
Preparation
Before data exchange is commenced, the parameters "Baud 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 Modbus
Slave responds after a request must be set. UNIGATE
®
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 GSD 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 field-
bus), 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.
Summary of Contents for UNIGATE MB EtherCAT
Page 2: ...Manual Art No V4044E ...
Page 60: ......
