K-Patents SeedMaster 2 - Manual (Page 85)

11 COMMUNICATION 85
85
(1byte)
11h 03h 80h 128 bytes CRC
•Function code: 16 (write), RTU mode
Write the first 32 data (64 registers, i. e. 128 bytes) into the „write data” table of the 2
nd
Crystallizer of SeedMaster 2 having station address 17 (11h):
Query:
Slave
address
Function
code
1
st
register
address
(high
byte)
1
st
register
address
(low
byte)
No of
registers
(high
byte)
No of
registers
(low
byte)
No of
bytes
(1 byte)
Data bytes CRC
code
(2
bytes)
11h 10h 00h 180h 00h 40h 80h 128 bytes CRC
Response:
Slave
address
Function
code
1
st
register
address
(high byte)
1
st
register
address
(low byte)
No of
registers
(high byte)
No of
registers
(low byte)
CRC
code
(2 bytes)
11h 10h 00h 00h 00h 40h CRC
Remark: Byte order on the MODBUS communication: High byte first, Low byte second.
11.3 Data types used in the MODBUS registers
A single MODBUS register has 2 bytes for data storage.
Byte (8 bit unsigned integer)
Low or high byte of a MODBUS register, value range 0…255 (00h…FFh)
Word (16 bit unsigned integer)
One MODBUS register can be a word type variable, value range 0 .. 65535 (0000h … FFFFh)
Real (FLOAT)
All of the SeedMaster 2 data / variables are 4 byte real type.
The real values have the standard IEEE 754/1985 SHORT REAL (SINGLE PRECISION) 4 byte format and
are stored in two consecutive registers.
The value range is +/-(8.43*10
-37
– 3.4*10
+38
), the resolution is 7 decimals.
Measured and calculated data of SeedMaster 2 are of the 4 byte real, IEEE standard type.
This way a SeedMaster 2 real (float) data can be accessed by reading 2 registers.
Data on the serial line reading a measured value:
First register: (reg1) Second register: (reg2)
High byte (reg1_Hi) Low byte (reg1_Lo) High byte (reg2_Hi) low byte (reg2_Lo)
The received bytes have to be arranged as shown below to form a real number:
MSB LSB
reg2_Hi reg2_Lo reg1_Hi reg1_Lo
The number format:
reg2_Hi reg2_Lo reg1_Hi reg1_Lo
Exponent (8bit) Mantissa (23 bit)
S:
Bit31 sign of the number, 0 if the real number is positive.