in a microcontroller with spi inteface a serial flash of type 25p640 of 64 mbit can be used externally can we use in this place the nand flash of 64 mbit externally
It depends on the interface that are available on the microprocessor.
SPI interface uses only 3 signals and can be easily implemented by software also on those microprocessor that do not integrate such a peripheral in the silicon.