Rainbow Electronics AT45DQ321 - Manual (Page 8)

8 AT45DQ321 [ADVANCE DATASHEET]
DS-45DQ321-031–DFLASH–12/2012
5. 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 see
Section 25., Detailed Bit-level
Read Waveforms: RapidS Mode 0/Mode 3 diagrams in this datasheet for details on the clock cycle sequences for each
mode.
5.1 Continuous Array Read (Legacy Command: E8h Opcode)
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 from memory to be performed without the
need for additional address sequences. To perform a Continuous Array Read using the standard DataFlash page size
(528 bytes), an opcode of E8h must be clocked into the device followed by three address bytes (which comprise the 23-bit
page and byte address sequence) and four dummy bytes. The first 13 bits (PA12 - PA0) of the 23-bit address sequence
specify which page of the main memory array to read and the last 10 bits (BA9 - BA0) of the 23-bit address sequence
specify the starting byte address within the page. To perform a Continuous Array Read using the binary page size
(512 bytes), an opcode of E8h must be clocked into the device followed by three address bytes and four dummy bytes.
The first 13 bits (A21 - A9) of the 22-bit address sequence specify which page of the main memory array to read and the
last 9 bits (A8 - A0) of the 22-bit address sequence specify the starting byte address within the page. The dummy bytes
that follow the address bytes are needed to initialize the read operation. Following the dummy bytes, 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 dummy bytes, and the reading of
data. When the end of a page in the 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 crossing 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 the data buffers and leaves the contents of the buffers unchanged.
5.2 Continuous Array Read (High Frequency Mode: 1Bh Opcode)
This command can be used to read the main memory array sequentially at the highest possible operating clock
frequency up to the maximum specified by f
CAR1
. To perform a Continuous Array Read using the standard DataFlash
page size (528 bytes), the CS pin must first be asserted, and then an opcode of 1Bh must be clocked into the device
followed by three address bytes and two dummy bytes. The first 13 bits (PA12 - PA0) of the 23-bit address sequence
specify which page of the main memory array to read and the last 10 bits (BA9 - BA0) of the 23-bit address sequence
specify the starting byte address within the page. To perform a Continuous Array Read using the binary page size (512
bytes), the opcode 1Bh must be clocked into the device followed by three address bytes (A21 - A0) and two dummy
bytes. Following the dummy bytes, 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 dummy bytes, and the reading of
data. When the end of a page in the 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 crossing 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.