4AT45DB1282 2472C–DFLSH–11/03
25-b it address sequ ence s pecify which page of the main mem ory array to read, and t he
last 11 bits (BA10 - BA0) of the 25-bit address sequence specify the starting byte
address within the page. The 24 or 19 don’t care clock cycles that follow the four
addres s bytes are needed t o initialize the read operat ion. Following the don’t c are clock
cycles, additional clock pulses on the SCK/CLK pin will result in data being output on
either the SO (serial output) pin or the eight output pins (I/O7- I/O0).
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
reache d duri ng a Continuous A rray Read, t he device wi ll continue reading at the begin-
ning o f the next pag e with no dela ys inc urred during the page bound ary crossover (th e
crossover from the end of one page to the beginning of the next page). When the last bit
(or byte if using the 8-bit interf ace mode) in the main m emory array has been read, t he
dev ice will con tinue reading bac k at the b eginni ng of the first page of mem ory. As w ith
cro ssing ov er page bou ndaries, no delays wi ll b e incurred wh en wrappin g around f rom
the end of the array to the begi nning of the array.
A low -to-hi gh tra nsition on the CS pin will terminat e the re ad operation and tri-state t he
output pins (SO or I/O7-I/O0). The maximum SCK/CLK frequency allowable for the Con-
tinuous Array Read is defined by the fCAR specification. The Continuous Array Read
bypa sses both data buffers and leave s the contents of the buffers unchanged.
MAIN MEMORY PAGE READ: A main memory page read allows the user to read data
directly from any one of the 16384 pages in the main memory, bypassing both of the
data buffers and leaving the contents of the buffers unchanged. To start a page read, an
opc ode o f D2H must be clo cked i nto th e devic e fol lowed by fou r addres s by tes (w hich
comprise 7 don’t care bits plus the 25-bit page and byte address sequence) and a series
of don’t care clock cycles (24 if using the serial interface or 19 if using the 8-bit inter-
face). The first 14 bits (PA13 - PA0) of the 25-bit address sequence s pecify the page in
main memory to be read, and the last 11 bits (BA10 - BA0) of the 25-bit address
sequence specify the starting byte address within that page. The 24 or 19 don’t care
cloc k c ycles th at fol low the four a ddres s by tes ar e sent to initi alize th e re ad ope ratio n.
Following the don’t care bytes, additional pulses on SCK/CLK result in data being output
on either the SO (serial output) pin or the eight output pins (I/O7 - I/O0). 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, the
device will continue reading back at the beginning of the same page. A low-to-high tran-
sition on the CS pin will terminate the read operation and tri-state the output pins (SO or
I/O7 - I/O0). The maxim um SCK/CLK frequency allowable for the Main Memory Page
Read is defined by the fSCK specificatio n. The Mai n Memory Page Read bypass es both
data buffe rs and leaves the contents of the buffers unchan ged.
BUFFE R READ : Data can be read from either one of the two buffers, using dif ferent
opcodes to specify which buffer to read from. With the serial interface, an opcode of
D4H is used to read data from buffer 1, and an opcode of D6H is used to read data from
buffer 2. Likewise with the 8-bit interface an opcode of 54H is used to read data from
buf fer 1 and a n opco de of 56H i s us ed to read d ata fr om b uffer 2 . To pe rform a bu ffer
read, the op code mu st be clo cked i nto the de vice follow ed by fou r add ress bytes com-
prised of 21 don’t care bits and 11 buffer address bits (BFA10 - BFA0). Following the
fou r address byte s, add itional don ’t care bytes (on e by te if using the seria l interface or
two byt es if u sing t he 8-bit interface) mus t be clocked in to initialize the read op eration.
Since the buffer size is 1056 bytes, 11 buffer address bits are required to specify the first
byte of dat a to be read from the bu ffer. The CS pin must remain low during the loadi ng
of the opcode, the address bytes, the don’t care bytes, and the reading of data. When
the end of a buffer is reache d, the device will continue reading back at the beginning of
th e buff er. A l ow-t o-hig h trans ition on the C S pin w ill te rmin ate th e read opera tion and
tri-state the output pins (SO or I/O7 - I/O0).