Elgas EDT 101, User Manual

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Address field
In a query frame, the address field contains a slave address. In a response frame, the address
field contains the address of the responding slave device.
Valid slave addresses are in the range of 1 – 247 decimal. Address 0 is reserved for broadcast
messages. Any query message with a slave address of 0 is a broadcast message which all slave
devices process but they do not generate any response.
Function field
In a query frame or a broadcast frame, the function field contains a function code, which
indicates the command to be performed. In a response frame, the function field contains a
copy of the function code received in the query. If the most significant bit in the function field
is set, an error occurred during the query processing. In this case the data field contains an
exception code that explains the particular error.
Data field
The data field contains information that is specific to each individual function.
CRC field
The CRC field contains a 16 bit CRC error check value that is used to verify the integrity of the
message frame.
4.2 Device Specific Features
4.2.1 Service Address
Due to the small dimensions of the transducer, no DIP switches or similar components can be
used for slave address setting. Instead, the slave address is software configurable. In some
cases, however, the slave address can be unknown. Thus, a service address 248 (dec) has been
assigned which the transducer always responds.
Any query frame with a slave address of 248 (dec) the transducer processes and generates a
response. The response is returned with the actual slave address in the address field instead
of the service address 248 (dec). When using the service address, only one transducer may be
connected on the bus with the only exception of the query with the “48h” function code as
described hereinafter in chapter
Chyba! Nenalezen zdroj odkazů. .
4.2.2 Communication Buffer Length
The transducer implements communication buffer 64 bytes long. If the length of the query
frame exceeds capacity of the buffer, the frame is flushed and no response is generated. If the
master requires such amount of data to be sent which exceeds the capacity of the buffer, the
response is truncated to the total frame length of 64 bytes.
4.2.3 Response Time
The transducer responds 4 to 20 ms after the last character of the query has been received.
The exact time of the response depends on the query length, response length and on the
function processed.