C
C-9GFK–0804B Appendix C RTU Protocol
Message Descriptions
The following pages explain the format and fields for each RTU message.

Message (01): Read Output Table

Format:
Address Func Error Check
01
Query
Address Func Error Check
01
Normal Response
Point No. Points
Starting Number of
Data
Hi Lo Hi Lo
Byte
Count
Query:
An address of 0 is not allowed as this cannot be a broadcast request.
The function code is 01.
The starting point number is two bytes in length. It may be any value less than the
highest output point number available in the Micro PLC. The starting point number
is equal to one less than the number of the first output point returned in the normal
response to this request.
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 Micro PLC. The high order byte of the starting point
number and number of bytes fields is sent as the first byte. The low order byte is the
second byte in each of these fields.
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 8 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, then the last data byte contains zeros in one to seven of its highest order bits.