You should use READMODBUS command to read 1 register at a time. Use it twice at two different addresses to read two registers:
DM[1] = READMODBUS(13, 1, 0)
DM[2] = READMODBUS(13, 1, 1)
The READMODBUS (13,xx,yy) means to use RTU command to read from COMM port #3 (RS485). xx is the ID of the RTU device, yy is the starting address of the register. The CRC16 is automatically generated by the READMODBUS command and need not be added.