Some implementations of Modbus reverse the two individual words of 32 bit data
and the data type specifiers “int32rev”, “uint32rev”, and “floatrev” are included to
accommodate those implementations. As an example, the value 1.0 is represented
with data type specifier float as 3F 80 00 00 while with data type specifier floatrev,
the same value is represented as 00 00 3F 80.
int32rev Treat four consecutive bytes as a thirty-two bit signed integer, least
significant word first
uint32, ulong Treat four consecutive bytes as a thirty-two bit unsigned integer
uint32rev Treat four consecutive bytes as a thirty-two bit unsigned integer, least
significant word first
bcd4 Treat two consecutive bytes as four binary coded decimal (bcd) digits
bcd8 Treat four consecutive bytes as eight binary coded decimal (bcd) digits
float Treat four consecutive bytes as a four byte IEEE format floating point
number
floatrev Treat four consecutive bytes as a four byte IEEE format floating point
number, least significant word first
Table 3-7. Modbus Data Type Specifiers (Cont’d)
Specifier Description
3-2. 

Modbus的一些实现将32位数据的两个单独的字反转
数据类型说明符“int32rev”、“uint32rev”和“floatrev”包括在
适应这些实现。例如，表示值1.0
数据类型说明符float为3F 80 00 00，而数据类型说明符floatrev，
相同的值表示为00 00 3F 80。
int32rev至少将四个连续字节视为32位有符号整数
重要单词优先
uint32，ulong将四个连续字节视为32位无符号整数
uint32rev至少将四个连续字节视为32位无符号整数
有意义的词优先
bcd4将两个连续字节视为四个二进制编码十进制（bcd）数字
bcd8将四个连续字节视为八个二进制编码十进制（bcd）数字
浮点将四个连续字节视为四字节IEEE格式的浮点
数字
floatrev将四个连续字节视为四字节IEEE格式的浮点
数字，首先是不重要的单词
表3-7。Modbus数据类型说明符（续）
说明符描述
3-2.