Rainbow Electronics AT45DB041D - Manual (Page 5)

5
3595R–DFLASH–11/2012
AT45DB041D
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 11 bits (PA10 - PA0) of the 20-bit address sequence specify which page of the main
memory array to read, and the last nine bits (BA8 - BA0) of the 20-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 11 bits (A18 - A8) of the 19-bits sequence specify which
page of the main memory array to read, and the last 8 bits (A7 - A0) of the 19-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
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 tri-state the output
pin (SO). The maximum SCK frequency allowable for the Continuous Array Read is defined by
the f
CAR1
specification. The Continuous Array Read bypasses both data buffers and leaves the
contents of the buffers unchanged.
6.2 Continuous Array Read (High Frequency Mode – 0BH): Up to 66MHz
This command can be used with the serial interface to read the main memory array sequentially
in high speed mode for any clock frequency up to the maximum specified by f
CAR1
. To perform a
continuous read array with the page size set to 264-bytes, the CS must first be asserted then an
opcode 0BH must be clocked into the device followed by three address bytes and a dummy
byte. The first 11 bits (PA10 - PA0) of the 20-bit address sequence specify which page of the
main memory array to read, and the last nine bits (BA8 - BA0) of the 20-bit address sequence
specify the starting byte address within the page. To perform a continuous read with the page
size set to 256-bytes, the opcode, 0BH, must be clocked into the device followed by three
address bytes (A18 - A0) and a dummy byte. Following the dummy byte, additional clock pulses
on the SCK pin will result in data being output on the SO (serial output) pin.