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GetIDN_S and GetIDN_P 2 bytes in TSXCSYxx and MMS Sercos Modules

Goals and Symptoms

The purpose of this resolution is to inform the user on the behavior when using the command GetIDN_S (opcode 1556) or Get IDN_P ( opcode 1557 ) from a Quantum (or) a Premium SERCOS Controller.

Facts and Changes

When a 2 bytes IDN is gets the PLC haven't any possibility to know if the value is signed or not. So, the PLC register accommodate values from -32767 to + 32767 in signed format
Due to the above reason, values for IDN_S ( or _P ) 2 bytes set higher than 32767 when read, will be returned as follows:

(i) 32768 -> -32768
(ii) 32769-> -32767
(iii) 35000 -> -30536 in signed format. Unsigned format will result in a huge number.

Causes and Fixes

When GetIDN_S ( or _P ) returns a negative value, it may be converted to its positive equivalent by adding 65536.
For example, -30536 + 65536 = 35000 and so on. There is no implication on using the SetIDN_S ( or _P) command for the same IDN which is Unsigned decimal format.

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