Rainbow Electronics AT45DB021E - Manual (Page 9)

9 AT45DB021E [PRELIMINARY DATASHEET]
8789B–DFLASH–11/2012
5.5 Main Memory Page Read
A Main Memory Page Read allows the user to read data directly from any one of the 1,024 pages in the main memory,
bypassing the data buffer and leaving the contents of the Buffer unchanged. To start a Main Memory Page Read using
the standard DataFlash page size (264 bytes), the CS pin must first be asserted then an opcode of D2h must be clocked
into the device followed by three address bytes
(which comprise the 24-bit page and byte address sequence) and
four dummy bytes. The first 10 bits (PA9 - PA0) of the 19-bit address sequence specify which page of the main memory
array to read, and the last nine bits (BA8 - BA0) of the 19-bit address sequence specify the starting byte address within
the page. To perform a Main Memory Page Read with the binary page size (256 bytes), the opcode D2h must be clocked
into the device followed by three address bytes (A17 - A0) and four dummy bytes. The first 10 bits (A17 - A8) of the
18-bit address sequence specify which page of the main memory array to read, and the last eight bits (A7 - A0) of the
18-bit address sequence specify the starting byte address within that page. The dummy bytes that follow the address
bytes are sent to initialize the read operation. Following the dummy bytes, the additional pulses on SCK 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. Unlike the Continuous Array Read command, when the end of a page in main memory is reached, the device will
continue reading back at the beginning of the same page rather than the beginning of the next page.
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 Main Memory Page Read is defined by the f
SCK
specification. The Main Memory Page
Read bypasses the data buffer and leaves the contents of the Buffer unchanged.
5.6 Buffer Read
The data buffer can be accessed independently from the main memory array, and utilizing the Buffer Read command
allows data to be sequentially read directly from the Buffer. Two opcodes, D4h or D1h, can be used for the Buffer Read
command. The use of each opcode depends on the maximum SCK frequency that will be used to read data from the
Buffer. The D4h opcode can be used at any SCK frequency up to the maximum specified by f
CAR
while the D1h opcode
can be used for lower frequency read operations up to the maximum specified by f
CAR2
.
To perform a Buffer Read using the standard DataFlash buffer size (264 bytes), the opcode must be clocked into the
device followed by three address bytes comprised of 15 dummy bits and nine buffer address bits (BFA8 -BFA0). To
perform a Buffer Read using the binary buffer size (256 bytes), the opcode must be clocked into the device followed by
three address bytes comprised of 16 dummy bits and eight address bits (A7 - A0). Following the address bytes, one
dummy byte must be clocked into the device to initialize the read operation if using opcode D4h. The CS must remain low
during the loading of the opcode, the address bytes, the dummy byte (for opcode D4h only), and the reading of data.
When the end of a buffer is reached, the device will continue reading back at the beginning of the Buffer. A
low-to-high transition on the CS pin will terminate the read operation and tri-state the output pin (SO).