Technical data

Linkage with PLC
108 VIPA GmbH CP486 ⋅ 00/14
6.2.3 Different Data Representation in Memory:
For the transfer of data between CP and PC, the different representation of words and doublewords
(extended words) on AT and PC (programmable controllers) has to be taken into account.
Unlike AT´s the PLC stores the datatype word in a different form in memory, High-Byte and Low-
Byte are stored reverse. In doublewords all 4 bytes are stored in exact reverse order. If data of type
word, doubleword is exchanged between PC and CP, it´s quite natural that an interchange has to be
undertaken, otherwise data is wrong after transmission. As far this is possible in a meaningful way
the COM-driver processes this adaptation automatically.
For data exchange via banks 0/1 the user has to execute the interchange on its own, either on the CP
or on the PC. The driver processes the interchange automatically for the banks 2/3 and bank 7 in all
cases.
Operation:
During transmission of bytes no interchange takes place.
During transmission of words High- Byte and Low-Byte are interchanged.
During transmission of extended words all 4 bytes are reversed according to their order.
Data representation in PC (programmable controller):
Address n Byte Representation Byte
Address n High-Byte
Address n+1 Low-Byte Representation Word
Address n High-Byte High-Word
Address n+1 Low-Byte High-Word
Address n+2 High-Byte Low-Word Repres. Doubleword
Address n+3 Low-Byte Low-Word
Data representation in AT
Address n Byte Representation Byte
Address n Low-Byte
Address n+1 High-Byte Representation Word
Address n Low-Byte Low-Word
Address n+1 High-Byte Low-Word
Address n+2 Low-Byte High-Word Repres. Doubleword
Address n+3 HighByte High-Word