DEUTSCHMANN AUTOMATION UNIGATE CL ProfibusDP, Инструкция по эксплуатации

Страница: 25 / 50

17.6.10 UNIGATE fieldbus gateway UNIGATE CL - ProfibusDP V. 2.3 25
Deutschmann Automation GmbH & Co. KG Implemented protocols in UNIGATE CL with Universal Script
10.3.4 Protocol type 3964
The difference to protocol type 3964R is:
1. tq = acknowledge monitoring time
2. The checksum byte BCC is missing.
10.4 Protocol: MODBUS-RTU
10.4.1 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.
10.4.2 UNIGATE as MODBUS-Master
10.4.2.1 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 10.5). 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.
If the "Length byte“ is activated (see chapter 10.6), the gateway transfers only the number of
bytes specified there. The number of received Modbus data items is saved in the direction of the
fieldbus Master. The length always refers to bytes "Address" to "Dat n" (inclusive in each case),
always without CRC checksum.