Device operation, Read commands – Rainbow Electronics AT45DB081D User Manual
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3596N–DFLASH–11/2012
AT45DB081D
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
through
. 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, tog-
gling 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 trans-
ferred with the most significant bit (MSB) first.
Buffer addressing for the DataFlash standard page size (264-bytes) is referenced in the data-
sheet using the terminology BFA8 - BFA0 to denote the nine address bits required to designate
a byte address within a buffer. Main memory addressing is referenced using the terminology
PA11 - PA0 and BA8 - BA0, where PA11 - PA0 denotes the 12 address bits required to desig-
nate a page address and BA8 - BA0 denotes the nine address bits required to designate a byte
address within the page.
For “Power of 2” binary page size (256-bytes) the Buffer addressing is referenced in the data-
sheet using the conventional terminology BFA7 - BFA0 to denote the eight address bits required
to designate a byte address within a buffer. Main memory addressing is referenced using the
terminology A19 - A0, where A19 - A8 denotes the 12 address bits required to designate a page
address and A7 - A0 denotes the eight address bits required to designate a byte address within
a page.
6.
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 protocols 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.
6.1
Continuous Array Read (Legacy Command: E8H): Up to 66MHz
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 from the DataFlash standard page
size (264-bytes), an opcode of E8H must be clocked into the device followed by three address
bytes (which comprise the 24-bit page and byte address sequence) and four don’t care bytes.
The first 12 bits (PA11 - PA0) of the 21-bit address sequence specify which page of the main
memory array to read, and the last nine bits (BA8 - BA0) of the 21-bit address sequence specify
the starting byte address within the page. To perform a continuous read from the binary page
size (256-bytes), the opcode (E8H) must be clocked into the device followed by three address
bytes and four don’t care bytes. The first 12 bits (A19 - A8) of the 20-bits sequence specify which
page of the main memory array to read, and the last eight bits (A7 - A0) of the 20-bits address
sequence specify the starting byte address within the page. The don’t care bytes that follow the
address bytes are needed to initialize the read operation. Following the don’t care bytes, addi-
tional 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