-31709 是HEX 的8423，错误代码一般用十六进制表示的，他表示：当写参数时产生了一个长度范围错误，下面是他的英文解释，
range length error when write a parameter ,this error indicates that the parameter x IS located either entirely or partly outside the range of an adrress or that the length of the bit range is not a multiple of 8 with an ANY parameter .