Appendices
A-22
CJ-series PROFIBUS Master Unit Operation Manual for NJ-series CPU Unit (W509)
• If the total number of bytes is an odd number, the Most Significant Byte of the last word is
filled with 0.
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 NJ-series controller double word format in the CPU memory area. The figure below
shows the conversion in graphic format.
PROFIBUS defines the IEEE 754 format single precision floating point data type. It is transferred over
the network as a 4 byte data, Most Significant Byte first. In the CPU 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 con-
version in graphic format.
PROFIBUS defines ASCII text strings data type. It is transferred over the network as a string of
characters. In order to maintain a readable string in the CPU memory, the data is converted to fit the
odd character in the Most Significant Byte of the words, and the even characters in the Least Signif-
icant Byte of the words. The string is stored on ascending word addresses in CPU memory. The fig-
ure below illustrates the conversion
A-6-2 Floating Point Data Conversions
A-6-3 Text String Data Conversion
Word 0
Word 1
CPU Data area
Byte 4 (LSB)Byte 3
Bit 15 Bit 00
Byte 2Byte 1 (MSB)
PROFIBUS
Double Word 0
Byte 1 (MSB)
Byte 2
Byte 3
Byte 4 (LSB)
Bit 07 Bit 00
CPU 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
Char 1
Char 2
CPU Data area PROFIBUS
Bit 07 Bit 00
Char n-1
Char n
Char 2Char 1
Bit 15 Bit 00
Word 0
Char nChar n-1Word m
ASCII Text string
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