Chapter 6. Serial I/O, SNP & RTU ProtocolsGFK-2222AD April 2018 237Message (02): Read Input TableFormat:Address StartingPoint No.Number ofPointsErrorCheckFunc02QueryHi HiLo LoAddress Data ErrorCheckFunc02Normal ResponseByteCountFigure 53: RTU Read Input Table Message FormatQuery:▪ 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 inputpoint number available in the attached CPU. The starting point number is equal to one less than thenumber of the first input point returned in the normal response to this request.▪ The number of points value is two bytes in length. It specifies the number of input points returned inthe normal response. The sum of the starting point value and the number of points value must beless than or equal to the highest input point number available in the attached CPU. The high orderbyte of the Starting Point Number and Number Of Bytes fields is sent as the first byte. The low orderbyte 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 normalresponse following the byte count and preceding the error check.▪ The Data field of the normal response is packed input status data. Each byte contains eight inputpoint values. The least significant bit (LSB) of the first byte contains the value of the input point whosenumber is equal to the starting point number plus one. The values of the input points are ordered bynumber starting with the LSB of the first byte of the Data field and ending with the most significantbit (MSB) of the last byte of the Data field. If the number of points is not a multiple of 8, then the lastdata byte contains zeroes in one to seven of its highest order bits.
