Crc; Device Compatibility Parameters - Emerson Mentor MP Advanced User's Manual

Parameter structure Keypad and display
Exception message format
The slave exception message has the following format.
Byte
0 Slave source node address
1 Original function code with bit7 set
2 Exception code
3 CRC LSB
4 CRC MSB
Exception codes
The following exception codes are supported.
Code
1 Function code not supported
Register address out of range, or request to read too many
2
registers
Parameter over range during block write FC16
The slave processes the write block in the order the data is received. If a
write fails due to an out of range value then the write block is terminated.
However, the slave does not raise an exception response, rather the
error condition is signalled to the master by the number of successful
writes field in the response.
Parameter over range during block read/write FC23
There will be no indication that there has been a value out of range
during a FC23 access.
6.2.9

CRC

The CRC is a 16bit cyclic redundancy check using the standard CRC-16
polynomial x16 + x15 + x2 + 1. The 16bit CRC is appended to the
message and transmitted LSB first.
The CRC is calculated on ALL the bytes in the frame.
6.2.10

Device compatibility parameters

All devices have the following compatibility parameters defined:
Parameter
Device ID Unique device identification code
Minimum slave response
time
When global addressing, the master
Maximum slave response
must wait for this time before issuing a
time new message. In a network of devices,
the slowest time must be used
Maximum baud rate
If this data type is not supported then an
32bit float data type
over range error will be raised if this data
supported
type is used
Maximum buffer size Determines the maximum block size.
210
Parameter description
Parameter x.00
Description
Description
Description
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Advanced parameter
format
descriptions
Serial comms
Performance
protocol
Mentor MP Advanced User Guide
Issue Number: 4