Rainbow Electronics AT45DB321B - Manual (Page 9)

9
AT45DB321B
2223D–DFLASH–10/02
WRITE PROTECT: If the WP pin is held low, the first 256 pages of the main memory
cannot be reprogrammed. The only way to reprogram the first 256 pages is to first drive
the protect pin high and then use the program commands previously mentioned. The
WP pin is internally pulled high; therefore, connection of the WP pin is not necessary if
this pin and feature will not be utilized. However, it is recommended that the WP pin be
driven high externally whenever possible.
RESET: A low state on the reset pin (RESET) will terminate the operation in progress
and reset the internal state machine to an idle state. The device will remain in the reset
condition as long as a low level is present on the RESET pin. Normal operation can
resume once the RESET pin is brought back to a high level.
The device incorporates an internal power-on reset circuit, so there are no restrictions
on the RESET pin during power-on sequences. The RESET pin is also internally pulled
high; therefore, connection of the RESET pin is not necessary if this pin and feature will
not be utilized. However, it is recommended that the RESET pin be driven high exter-
nally whenever possible.
READY/BUSY: This open drain output pin will be driven low when the device is busy in
an internally self-timed operation. This pin, which is normally in a high state (through
a 1 k
W
external pull-up resistor), will be pulled low during programming operations, com-
pare operations, and during page-to-buffer transfers.
The busy status indicates that the Flash memory array and one of the buffers cannot be
accessed; read and write operations to the other buffer can still be performed.
Power-on/Reset State
When power is first applied to the device, or when recovering from a reset condition, the
device will default to SPI Mode 3. In addition, the SO pin will be in a high-impedance
state, and a high-to-low transition on the CS pin will be required to start a valid instruc-
tion. The SPI mode will be automatically selected on every falling edge of CS by
sampling the inactive clock state.