This unit uses an array of bytes to represent a LARGE number. The number is binairy-stored in the array, with the Least Significant Byte (LSB) first and the Most Significant Byte (MSB) last, like all Intel-integer types.
/*SPI规范：Data is always clocked into the device on the rising edge of SCK a-*/
/* nd clocked out of the device on the falling edge of SCK.All instruction-*/
/* s,addresses and data are transferred with the most significant bit(MSB) */
/* first.
