Скорее всего стоит запрет на запись
The write disable (WDS) instruction disables all programming
capabilities. This protects the entire part against
accidental modification of data until a WEN instruction is
executed. (When Vcc is applied, this part powers up in the
write disabled state.) To protect data, a WDS instruction
should be executed upon completion of each programming
operation. (NOTE: Neither the WEN nor the WDS
instruction has any effect on the READ instruction.)
http://files.ddrservice.info/Memory/spi/93c46_3.pdf