Winbond External Flash serial NOR memory unit

The Status Register 1 busy flag bit doesn't function as expected. It reads 0 even when the External Flash Erase operation is not complete. To confirm this, certain bytes of data was written from the start address of two successive sectors i.e at 0x00000000 (sector1) and at 0x00001000(sector2) after which 2 successive sector erase operations were issued and then the contents of the two sectors were read back. Out of the two sector erase commands (issued for the same two sectors) only the first erase command actually erases the Flash content but the second one doesn't. The read operation returned the data in the sector 2.

When the above trail was tried using a 250 ms delay between the two successive sector erase operations, both the erase operations erased the flash contents as expected. The conclusion is that this is an unexpected behavior owing to the improper functioning of busy flag in Status Register 1. The observations made using logic analyzer shows that the busy flag is returning 0 after a certain duration, but that duration is probably smaller than the duration the external flash requires to actually complete the sector erase operation.