K-Patents SeedMaster 2 - Manual (Page 81)

11 COMMUNICATION 81
81
25 00 00 00 00 1B 15 header, ID = 15 (hex)
03 command code (READ)
18 number of bytes = 18 (hex) = 24 (dec)
6B 85 42 9D 85 1F data (24 (dec) bytes)
42 8B 97 ED 44 B7
1B (hex) = 27 (dec) 6E CC 42 AC 00 00
bytes follow 00 00 00 00 00 00
18 (hex) bytes
Client’s request to WRITE REGISTERS:
0F 00 00 00 00 0E 15 10 00 80 04 08 80 00 42 9E 8A 3D 42 8D
complete message
0F 00 00 00 00 0E 15 header, SeedMaster 2 ID = 15
10 command code (WRITE)
00 80 register base address
04 number of registers
08 number of bytes
80 00 42 9E 8A 3D 42 8D data
The Client requests writing the 8 data bytes in the registers of SeedMaster 2 with MODBUS address 15 (hex)
starting from base address 0080 (hex).
SeedMaster 2 will acknowledge the request with the following message:
0F 00 00 00 00 06 15 10 00 80 00 04
complete message
0F 00 00 00 00 06 15 header, SeedMaster 2 ID = 15
10 command code (WRITE)
00 80 register base address
00 04 number of registers
Numbers in the MODBUS registers
Storage of data in the MODBUS registers: Hbyte Lbyte
WORD data
This type of data is stored in 2 bytes (16 bits). There is no sign stored and the range is 0 – 65535.
MODBUS REGISTER
HIGH byte LOW byte
Most Significant Bit Least Significant Bit
15 0
FLOATING POINT data
Floating point data in SeedMaster 2 comply with the IEEE 754 / 1985 SHORT REAL (SINGLE PRECISION)
format specification. The number consists of 3 parts:
•
sign,
•
exponent and
•
mantissa,
which are stored in 4 bytes. Consequently, storage of floating point numbers requires 2 MODBUS registers.
High address MODBUS register Low address MODBUS register
High byte Low byte High byte Low byte
S Exponent Mantissa
31 30 23 22 0
The value of the sign bit S is 0, if the number is positive, and 1, if it is negative. Due to the fact that the
numbers do not use the 2-s complement notation, + 0 and – 0 are also represented.
The Mantissa is stored in normalized form which means that:
bit 22 = 2
-1
, bit 21 = 2
-2
, … , and bit 0 = 2
-23
.