Memory system and control method based on quad-serial peripheral interface (SPI) controller with external memory system based on SPI standard

A method for controlling a memory system including a nonvolatile memory, a first terminal, and a second terminal with a serial peripheral interface (SPI) controller with an external controller external to the memory system in accordance with an SPI standard, the method comprising:

• receiving a command through the first terminal;
• determining an operational mode of the SPI controller to be one of a plurality of operational modes including a first mode and a second mode, based on the command;
• upon determining the operational mode to be the first mode, operating in the first mode in which a signal received through the second terminal is used as a control signal to perform a predetermined function;
• and
• upon determining the operational mode to be the second mode, operating in the second mode in which the signal received through the second terminal is not used as the control signal to perform the predetermined function, wherein the method further comprises, in the second mode;
• using a second signal of a predetermined length received through the first terminal following the command as an address of the nonvolatile memory to be accessed;
• and
• performing an operation to disable the predetermined function during reception of the second signal used as the address through the first terminal.