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I/O Data Conversions Appendix D
• The first two bytes are stored in the lowest word of the destination data block in PLC Memory word. Every
consecutive two bytes are stored in the next higher words.
• Odd byte numbers are copied to the Least Significant byte of a PLC Memory word.
• Even byte numbers are copied to the Most Significant Byte of a PLC Memory word.
• If the total number of bytes is an odd number, the Most Significant Byte of the last word is filled with 0.
16-bit Word Data
16-bit word data is transferred over PROFIBUS with the Most Significant Byte first. The PROFIBUS Master Unit
will ensure that a word transmitted or received over PROFIBUS is mapped to one word in the PLC Memory
Area. The figure below shows the conversion in graphic format.
32-bit Double Word Data
32-bit double word data is transferred over PROFIBUS with the Most Significant Byte first. The PROFIBUS
Master Unit will ensure that a double word transmitted or received over PROFIBUS is mapped on to CS1/CJ1-
series double word format in the PLC Memory Area. The figure below shows the conversion in graphic format.
D-3 Floating Point Data Conversions
PROFIBUS defines the IEEE 754 format single precision floating point data type. It is transferred over the net-
work as a 4 byte data, Most Significant Byte first. In the PLC Memory Area the same data type and size is
defined, but data of this type is stored with the Most Significant bytes on the higher memory location and the
Least Significant Bytes on the lower memory location. The figure below shows the conversion in graphic for-
mat.
Word 0
PLC Data area
PROFIBUS
Word
Byte 0 (MSB)
Byte 1 (LSB)
Bit 07 Bit 00
Byte 1 (LSB)Byte 0 (MSB)
Bit 15 Bit 00
Word 0
Word 1
PLC Data area
Byte 3 (LSB)Byte 2
Bit 15 Bit 00
Byte 1Byte 0 (MSB)
PROFIBUS
Double Word 0
Byte 0 (MSB)
Byte 1
Byte 2
Byte 3 (LSB)
Bit 07 Bit 00
PLC Data area
Byte 4 (LSB)Byte 3
Bit 15 Bit 00
Byte 2Byte 1 (MSB)
PROFIBUS
Single precision
floating point
(IEEE754)
Byte 1 (MSB)
Byte 2
Byte 3
Byte 4 (LSB)
Bit 07 Bit 00
Word 0
Word 1
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