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After the CRC code is acquired through the above-mentioned method, attach it to the
transmitted data and send them. It is necessary to exchange the high and low bytes of
the CRC code, namely, to send the low byte firstly and then the high byte.
There are two methods to compute CRC code with software: table look-up and on-line
computation. Computation speed of the table look-up is fast but its table data occupy
considerable space; On-line computation method requires no table data. It saves space
but needs much time. Suitable computation method is selected according to concrete
circumstance during application.
A2.4 Error code
When the slave is not able to implement master’s request, the slave gives feedback of
corresponding error code to indicate cause of the current error. Refer to the following
table for the concrete meaning of error code.
Table A.9 Description of error code
Error code
Description
Command code error
01
● Command code other than 03H and 06H is set in the request
message
Communication address error
02
● Visited communication address does not exist.
● The register corresponding to the communication address does not
permit performance of the action demanded by the current command
code.
Data setting error
03
● Written data exceeds the allowable range of the register.
● Improper setting of certain parameter in the request message.
Unable to continue implementing the master’s request.
04
● Error occurs during the process of writing data.
● Currently the register corresponding to the communication address
does not permit performance of the action demanded by the
command code.
