Endress+Hauser EngyVolt RV12, Руководство по эксплуатации

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Appendix EngyVolt RV12
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Exception response
If an error is detected in the content of the query (excluding parity errors and error check
mismatch), then an error response (called an exception response), will be sent to the
master. The exception response is identified by the function code being a copy of the query
function code but with the most-significant bit set. The data contained in an exception
response is a single byte error code.
First Byte Last Byte
"Slave" address Function code Error code Error check (Lo) Error check (Hi)
"Slave" address:
8-bit value representing the address of slave that is responding.
Function code:
8 bit value which is the function code in the query OR'ed with 80 hex, indicating that the
slave either does not recognize the query or could not carry out the action requested.
Error code:
-bit value indicating the nature of the exception detected, see table of error codes
(→  54).
Error check (Lo):
The bottom (least significant) eight bits of a 16-bit number representing the error check
value.
Error check (Hi):
The top (most significant) eight bits of a 16-bit number representing the error check value.
11.4.2 Serial transmission modes
There are two Modbus Protocol serial transmission modes, ASCII and RTU. EngyVolt
devices do not support the ASCII mode.
In RTU (Remote Terminal Unit) mode, each 8-bit byte is used in the full binary range and
is not limited to ASCII characters as in ASCII Mode. The greater data density allows better
data throughput for the same baud rate, however each message must be transmitted in a
continuous stream. This is very unlikely to be a problem for modern communications
equipment.
Coding system Full 8-bit binary per byte. In this document, the value of each byte will be shown as two
hexadecimal characters each in the range 0-9 or A-F.
Line protocol 1 start bit, followed by the 8 data bits. The 8 data bits are sent with least significant bit
first.
User option of parity
and stop bits: a) no parity & 2 stop bits
b) no parity & 1 stop bit
c) even parity & 1 stop bit
d) odd parity & 1 stop bit
User option of baud
rate a) 2 400 b) 4 800
c) 9 600 d) 19 200
The baud rate, parity and stop bits must be selected to match the master’s settings.