Chapter 6. Serial I/O, SNP & RTU Protocols
GFK-2222AD
April 2018
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Message (15): Force Multiple Outputs
Format:
Address
Number
of Points
Error Check
Func
15
Query
Normal Response
Address
Error Check
Func
15
Byte
Count
Data
Starting
Point
Point No.
Number
of Points
Starting
Point
Point No.
Figure 60: RTU Force Multiple Outputs Message Format
Query:
▪
An Address of 0 indicates a broadcast request. All slave stations process a broadcast request and no
response is sent.
▪
The value of the Function code is 15.
▪
The Starting Point Number is two bytes in length and may be any value less than the highest output
point number available in the attached CPU. The Starting Point Number is equal to one less than the
number of the first output point forced by this request.
▪
The Number of Points value is two bytes in length. The sum of the Starting Point Number 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 Bytes fields is
sent as the first byte in each of these fields. The low order byte is the second byte in each of these
fields.
▪
The Byte Count is a binary number from 1 to 256 (0 = 256). It is the number of bytes in the Data field
of the force multiple outputs request.
▪
The Data field is packed data containing the values that the outputs specified by the Starting Point
Number and the Number of Points fields are to be forced to. Each byte in the Data field contains the
values that eight output points are to be forced to. The least significant bit (LSB) of the first byte
contains the value that the output point whose number is equal to the starting point number plus
one is to be forced to. The values for 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, then the last data byte contains zeroes in
one to seven of its highest order bits.
Response:
▪
The descriptions of the fields in the response are covered in the query description.
Note:
The force multiple outputs request is not an output override command. The outputs
specified in this request are ensured to be forced to the values specified only at the beginning
of one sweep of the user logic.
