15

3387L–DFLASH–6/06

AT45DB321C

If a Group A mode is in progress (not fully completed), then another mode in Group A should not

be started. However, during this time in which a Group A mode is in progress, modes in Group B

can be started, except the first two Group A commands (Memory Array Read Commands).

This gives the DataFlash the ability to virtually accommodate a continuous data stream. While

data is being programmed into main memory from buffer 1, data can be loaded into buffer 2 (or

vice versa). See application note AN-4 (“Using Atmel’s Serial DataFlash”) for more details.

7.4

Pin Descriptions

7.4.1

Serial Input (SI)

The SI pin is an input-only pin and is used to shift data serially into the device. The SI pin is used

for all data input, including opcodes and address sequences.

7.4.2

Serial Output (SO)

The SO pin is an output-only pin and is used to shift data serially out from the device.

7.4.3

Serial Clock (SCK)

The SCK pin is an input-only pin and is used to control the flow of data to and from the

DataFlash. Data is always clocked into the device on the rising edge of SCK and clocked out of

the device on the falling edge of SCK.

7.4.4

Chip Select (CS)

The DataFlash is selected when the CS pin is low. When the device is not selected, data will not

be accepted on the input pin (SI), and the output pin (SO) will remain in a high impedance state.

A high-to-low transition on the CS pin is required to start an operation, and a low-to-high transi-

tion on the CS pin is required to end an operation or to start an internally self-timed operation.

7.4.5

Write Protect (WP)

The WP pin is used to control the Hardware Sector Protection. Hardware Sector Protection is

enabled by asserting the WP pin and keeping the pin in it’s asserted state. Disabling Hardware

Sector Protection is accomplished by simply deasserting the WP pin. The WP pin will override

the software controlled sector protection method but only for protecting the sectors. For exam-

ple, if the sectors were not previously protected by the Enable Sector Protection command, then

simply asserting the WP pin for the minimum specified time (t

tection. When the WP pin is deasserted; however, the sector protection would no longer be

enabled as long as the Enable Sector Protection command was not issued while the WP pin was

asserted. If the Enable Sector Protection command was issued before or while the WP pin was

asserted, then simply deasserting the WP pin would not disable the sector protection. In this

case, the Disable Sector Protection command would need to be issued while the WP pin is

deasserted to disable the sector protection. The Disable Sector Protection command is also

ignored whenever the WP pin is asserted.

To ensure backwards compatibility with previous generations of DataFlash, the function of the

WP pin has not changed. Therefore, when the WP pin is asserted, certain sectors in the memory

array will be protected, and when the WP pin is deasserted, the memory array will be unpro-

tected provided the Enable Sector Protection command hasn’t been issued. New devices are

shipped from Atmel with the contents of the Sector Protection Register pre-programmed with

“00H” (unprotect). The user can reprogram the Sector Protection Register to change which sec-

tors will be protected by the WP pin.