SA25F020 Datasheet, PDF (24/37 Pages) List of Unclassifed Manufacturers – 2Mb Serial Flash with 25MHz SPI Bus Interface

Fast Read (FAST_READ)
The Fast Read instruction is included in the
device in order for it to be compatible with
other SPI Flash devices. Both the READ
and FAST_READ instructions read the
memory at the specified SCK frequency
(F_SCK), with a maximum speed of 25 MHz.
Reading the memory via the serial SPI link
requires the following sequence:
1. After the CSb line is pulled low to
select the device, the READ
opcode is transmitted via the SI
line, followed by the 3-byte address
and a dummy byte (address bits
A23 to A18 are Don’t Care).
2. Upon completion, any data on the
SI line is ignored.
SA25F020 Advanced Information
SAIFUN
24
3. The data (D7-D0) at the specified
address is then shifted out onto the
SO line. Each bit is shifted out at a
maximum frequency of F_SCK.
If only one byte is to be read, the CSb line
should be driven high after the data comes
out. The READ sequence can be
continued, as the byte address is
automatically incremented and data
continues to shift out. When the highest
address is reached, the address counter
rolls over to the lowest address, enabling
the entire memory to be read in one
continuous READ cycle. The instruction
sequence is shown in Figure 15.
Driving CSb high terminates the
FAST_READ instruction, which can be
done at any time during data output. Any
FAST_READ instruction executed while an
Erase or Program cycle is in progress is
rejected without having any effect on the
cycle in progress.
CS
SCK
0 1 2 3 4 5 6 7 8 9 10 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47
Instruction
24-Bit
Address
Dummy Byte
SI
23 22 21
321076543210
SO
High Impedance
DATA OUT 1
DATA OUT 2
7 6 54 3 2 1 07
MSB
MSB
Figure 15. Fast Read (FAST_READ) Instruction Sequence