PACSystems™ RX3i and RSTi-EP CPU Reference Manual Section 6
GFK-2222AK October 2019
Serial I/O, SNP & RTU Protocols 171
▪ The number of points value is two bytes in length. It specifies the number of output
points returned in the normal response. The sum of the starting point value and the
number of points value must be less than or equal to the highest output point
number available in the attached CPU. The high order byte of the Starting Point
Number and Number of Points fields is sent as the first byte. The low order byte is
the second byte in each of these fields.
6.3.3.1.3 Response:
The byte count is a binary number from 1 to 256 (0 = 256). It is the number of bytes in the
normal response following the byte count and preceding the error check.
The Data field of the normal response is packed output status data. Each byte contains
eight output point values. The least significant bit (LSB) of the first byte contains the value
of the output point whose number is equal to the starting point number plus one. The
values of the output points are ordered by number starting with the LSB of the first byte
of the Data field and ending with the most significant bit (MSB) of the last byte of the
Data field. If the number of points is not a multiple of 8, the last data byte contains zeroes
in one to seven of its highest order bits.
6.3.3.2 Message (02): Read Input Table
6.3.3.2.1 Format:
Figure 24: RTU Read Input Table Message Format
6.3.3.2.2 Query:
▪ An address of 0 is not allowed as this cannot be a broadcast request.
▪ The function code is 02.
▪ The starting point number is two bytes in length and may be any value less than the
highest input point number available in the attached CPU. The starting point number
is equal to one less than the number of the first input point returned in the normal
response to this request.
To Next Page
Loading...
Need help?
General
