Table of Contents
Advertisement
Modbus RTU Communication
Range 40.000 a 40.140
and operating conditions, also in size 32 bits with the floating point type of single precision (standard IEEE 754).
The parameter 40140 (serial number) is special and must be read as integer 32 bits.
7.3
SERIAL TRANSMISSION
In the protocol specification two transmission modes, ASCII and RTU are defined, which define how the bytes of
the message are transmitted. However, the ECW500 only uses the RTU mode for the transmission of
telegrams.
The ECW500 uses an RS-485 interface that can be configured as Half Duplex or Full Duplex via parameter
30002. In the parameter table of chapter 1 you can check all the options for configuring this communication
interface (parameters 30006 to 30014).
7.3.1
Time Between Messages
In the RTU mode
indication of when a new message starts or when it finishes is done by the absence of data transmission in the
network for a minimum period of 3.5 times the time of transmission of a data byte (11 bits). Thus, if a telegram is
started after the occurrence of this minimum period, the network elements will assume that the first character
received represents the beginning of a new telegram. And, likewise, the network elements will assume that the
telegram reached the end when, after receiving the bytes of the telegram, this period elapses again.
If during the transmission of a telegram, the period between the bytes is longer than this minimum period, the
telegram will be considered invalid, because the ECW500 will discard the bytes already received and build a
new telegram with the bytes that are being transmitted.
For a baud rates above 19200 bits/s, the times used are the same ones considered for this rate. Table 7.1
shows the times for different baud rates:
In which:
T
T
7.3.2
Physical Interface
The RS485 physical interface for communication of the ECW500 in the MODBUS RTU network is internally
isolated and consists of 5 marked terminals, as follows, according to the label on the side of the product.
COMMUNICATION
Connector Number
The RS-485 interface of the ECW500 also allows half duplex and full duplex connections. In the Half Duplex
mode, only the terminals RxB and RxA (the GND terminal can also be used if necessary) are used for both
transmission and reception of data for communication with the MODBUS network master. In the Full Duplex
mode, all terminals are used in the communication. The terminals RxA and RxB are used to receive data from
the network master, and terminals TxA and TxB are used to transmit the data to the MODBUS network master.
To communicate with computers is necessary to use an USB converter (or a RS232 converter, if this interface is
available).
WEG offers as an accessory the USB-i485 converter (Figure 7.1), which can be purchased directly or through
one of its representatives, by the code 11511558.
60 | ECW500
Registers read-only. These are the variables that present the ECW500 measurements
a specific character that indicates the beginning or the end of a telegram. The
Table 7.1 Baud rates and times involved in telegram transmission
Baud Rate
9600 bits/s
19200 bits/s
38400 bits/s
57600 bits/s
time to transmit a word of the telegram
11bits
Minimum interval to indicate the beginning and end of telegram (3.5 x T
3,5x
2
Identification
GND
T
11bits
1,146 ms
4,010 ms
2,005 ms
2,005 ms
2,005 ms
COM 1
3
4
TxB(-)
TxA(+)
RxB(-)
T
3,5x
)
11bits
5
6
RxA(+)
.
Advertisement
Table of Contents
