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C700 | C720 Series Operating Manual
The request frame and response frame are illustrated below in two registers that write the values 0x000A and 0x0102
to the start address of 2.
Request Frame
Number Systems
Function code
Start address (high byte)
Start address (low byte)
Number of Read Registers (High Bytes)
Number of Read Registers (Low Bytes)
Number of bytes
Register value (high byte)
Register value (low byte)
Register value (high byte)
Register value (low byte)
Figure 13: Examples of writing multiple register request and response frames
Data Format
Overview
Floating Point
Definition : Floating point, conforming to IEEE 754 (single precision)
Description
Symbol
Bit
3
Index Deviation
127
Figure 14: floating point single-precision definition (4 bytes, 2 MODBUS registers)
Example:
Compile decimal 17.625 to binary
Step 1:
Converting 17.625 in decimal form to a floating-point number in binary form, first finding the binary representation of the integer
part 17 Decimal= 16 + 1 = 1×24 + 0×23 + 0×22 + 0×21 + 1×20
The binary representation of integer part 17 is 10001B then the binary representation of decimal part is obtained 0.625= 0.5 + 0.125 = 1×2-1 +
0×2-2 + 1×2-3
The binary representation of decimal part 0.625 is 0.101B.
So the binary floating point number of 17.625 in decimal form is 10001.101B
Step 2:
Shift to find the exponent.
Move 10001.101B to the left until there is only one decimal point, resulting in 1.0001101B, and 10001.101B = 1.0001101 B× 24 . So the exponential
part is 4, plus 127, it becomes 131, and its binary representation is 10000011B.
Step 3:
Calculate the tail number
After removing 1 before the decimal point of 1.0001101B, the final number is 0001101B (because before the decimal point must be 1, so IEEE
stipulates that only the decimal point behind can be recorded). For the important explanation of 23-bit mantissa, the first (i.e. hidden bit) is
not compiled.
Hidden bits are bits on the left side of the separator, which are usually set to 1 and suppressed.
Step 4:
Symbol bit definition
The sign bit of positive number is 0, and the sign bit of negative number is 1, so the sign bit of 17.625 is 0.
Step 5:
Convert to floating point number
1 bit symbol + 8 bit index + 23-bit mantissa 0 10000011 00011010000000000000000B
(the hexadecimal system is shown as 0 x418d0000)
(hexidecimal)
0x10
0x00
0x01
0x00
0x02
0x04
0x00
0x0A
0x01
0x02
Index
Mantissa
30...23
22...0
Response Frame
Function code
Register Value (High Bytes) (108)
Register Value (Low Bytes)(108)
Register Value (High Bytes) (109)
Register Value (Low Bytes) (109)
Register Value (High Bytes)(110)
SUM
22...0
◀ ◀
26
|
(hexidecimal)
0x10
0x00
0x01
0x00
0x02
0x00
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