4

3387L–DFLASH–6/06

AT45DB321C

5.

Device Operation

The device operation is controlled by instructions from the host processor. The list of instructions

and their associated opcodes are contained in Tables 1 through 4. A valid instruction starts with

the falling edge of CS followed by the appropriate 8-bit opcode and the desired buffer or main

memory address location. While the CS pin is low, toggling the SCK pin controls the loading of

the opcode and the desired buffer or main memory address location through the SI (serial input)

pin. All instructions, addresses, and data are transferred with the most significant bit (MSB) first.

Buffer addressing is referenced in the datasheet using the terminology BFA9-BFA0 to denote

the 10 address bits required to designate a byte address within a buffer. Main memory address-

ing is referenced using the terminology PA12-PA0 and BA9-BA0, where PA12-PA0 denotes the

13 address bits required to designate a page address and BA9-BA0 denotes the 10 address bits

required to designate a byte address within the page.

5.1

Read Commands

By specifying the appropriate opcode, data can be read from the main memory or from either

one of the two SRAM data buffers. The DataFlash supports RapidS protocol for Mode 0 and

Mode 3. Please refer to the “Detailed Bit-level Read Timing” diagrams in this datasheet for

details on the clock cycle sequences for each mode.

5.1.1

Continuous Array Read

By supplying an initial starting address for the main memory array, the Continuous Array Read

command can be utilized to sequentially read a continuous stream of data from the device by

simply providing a clock signal; no additional addressing information or control signals need to

be provided. The DataFlash incorporates an internal address counter that will automatically

increment on every clock cycle, allowing one continuous read operation without the need of

additional address sequences. To perform a continuous read, an opcode of E8H must be

clocked into the device. The opcode is followed by three address bytes (which comprises 24-bit

page and byte address sequence) and 32 don’t care clock cycles. The first bit of the 24-bit

address sequence is reserved for upward and downward compatibility to larger and smaller den-

sity devices (see the notes under Section 13.6 on page 25. The next 13 bits (PA12-PA0) of the

24-bit address sequence specify which page of the main memory array to read, and the last

10 bits (BA9-BA0) of the 24-bit address sequence specify the starting byte address within the

page. The 32 don’t care clock cycles that follow the four address bytes are needed to initialize

the read operation. Following the don’t care clock cycles, additional clock pulses on the SCK pin

will result in data being output on the SO (serial output) pin.

The CS pin must remain low during the loading of the opcode, the address bytes, the don’t care

bytes, and the reading of data. When the end of a page in main memory is reached during a

Continuous Array Read, the device will continue reading at the beginning of the next page with

no delays incurred during the page boundary crossover (the crossover from the end of one page

to the beginning of the next page). When the last bit in the main memory array has been read,

the device will continue reading back at the beginning of the first page of memory. As with cross-

ing over page boundaries, no delays will be incurred when wrapping around from the end of the

array to the beginning of the array.

A low-to-high transition on the CS pin will terminate the read operation and tristate the output pin

(SO). The maximum SCK frequency allowable for the Continuous Array Read is defined by the

f

tents of the buffers unchanged.