Error and exception responses, Address range, 2 error and exception responses – West Control Solutions N6600 User Manual

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Loopback Diagnostic Test

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This is an eight-byte message comprising the usual pre-amble, a two-byte

diagnostic code, two bytes of data and the CRC16 bytes:

The only diagnostic code supported is 00. The normal response is an exact echo

of the received message.

Preset Multiple Registers

(Write n Words) - 16

This is an eleven-byte message. only one parameter may be written for each

received message. The usual pre-amble is followed by the address of the

parameter to be written, a two-byte word count (always set to 1), a single-byte

byte count (always set to 2), the value to be written and the CRC16 bytes:

The Controller normally responds with the following eight-bit reply:

4.3.2 Error and Exception Responses

If a received message contains a corrupted character (parity check failure,

framing error etc.) or if the CRC16 check fails, or if the received message is

otherwise syntactically flawed (e.g. byte count or word count is incorrect), the

Controller will ignore that message.

If the received message is syntactically correct but nonetheless contains an illegal

value, the Controller will send a five-byte exception response as follows:

The Function Number byte contains the function number contained in the

message which caused the error, with its top bit set (i.e. Function 3 becomes 0x83)

and the Exception Number is on of the following codes:

NOTE: Writing a parameter value equal to its current value is a valid

transaction; this will not cause an error response.

4.3.3 Address Range

With standard RS485 communications configured, the selectable address range is

1 - 128. With enhanced RS485 communications configured, the selectable

address range is 1 - 255. The Controller will respond appropriately to Address 0 -

broadcast messages - no matter what address is selected.

NOTE: The total receiver load on the RS485 link must not exceed 32

standard RS485 unit loads. This applies to both standard and enhanced

RS485 communications. A Plastics Controller presents

standard RS485

load, so a maximum of 128 Controllers are permitted. With other devices

O075-4

4-5

PM-0075