# Usage of the PKW protocol

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· A request or a response can only ever refer to one parameter.

· The complete request must be sent in one telegram. Request telegrams cannot be split. The

same applies to responses.

· The request identifier (AK) has to correspond to the data type of the parameter. Use the array

request identifier 6, 7 and 8 only for parameter with more then one index (array).

Parameter data type | Possible request identifier | Comment
1 Byte Integer (signed and unsigned) | 1: Request parameter value 2: Modify parameter value (word) 6: Request parameter value (array) 7: Modify parameter value (array, word) 9: Request number of array elements |
2 Byte Integer (signed and unsigned) | 1: Request parameter value 2: Modify parameter value (word) 6: Request parameter value (array) 7: Modify parameter value (array, word) 9: Request number of array elements |
4 Byte Integer (signed and unsigned) | 1: Request parameter value 3: Modify parameter value (double word) 6: Request parameter value (array) 8: Modify parameter value (array, double word) 9: Request number of array elements | The lower two bytes of the parameter values are in PWE2 and the higher two bytes in the PWE1.
Floating Point | 1: Request parameter value 3: Modify parameter value (double word) 6: Request parameter value (array) 8: Modify parameter value (array, double word) 9: Request number of array elements | The floating-point value is in the IEEE 754 format. This is an industry standard for representing floating-point numbers. The lower two bytes of the floating-point parameter value are in PWE2 and the higher two bytes in the PWE1.

· The master must repeat a request continuously until it has received the appropriate response. The

master detects the response to a request it has sent by:

evaluating the response identifier (see Table 1)

evaluating the parameter number PNU

evaluating the parameter index IND (only for array parameters)

evaluating the parameter value PWE (for modify requests (AK = 2, 3, 7 or 8))

· In the case of response telegrams which contain parameter values (request of parameter values),

the valve always returns the momentary parameter value when repeating response telegrams.

That means that the master can monitor a parameter value over a long time by repeating the

same telegram.

· If no information needs to be fetched from the PKW, then the "No request" request telegram must

be issued.

· If the response identifier is “Not possible to process request” (value 7) there is an additional error

code in the PWE2 response. Please refer to Table 3.