W25X10A, W25X20A, W25X40A, W25X80A
9. FUNCTIONAL DESCRIPTION
9.1
SPI OPERATIONS
9.1.1 SPI Modes
The W25X10A/20A/40A/80A is accessed through an SPI compatible bus consisting of four signals:
Serial Clock (CLK), Chip Select (/CS), Serial Data Input/Output (DIO) and Serial Data Output (DO).
Both SPI bus operation Modes 0 (0,0) and 3 (1,1) are supported. The primary difference between
Mode 0 and Mode 3 concerns the normal state of the CLK signal when the SPI bus master is in
standby and data is not being transferred to the Serial Flash. For Mode 0 the CLK signal is normally
low. For Mode 3 the CLK signal is normally high. In either case data input on the DIO pin is sampled
on the rising edge of the CLK. Data on the DO and DIO pins are clocked out on the falling edge of
CLK.
9.1.2 Dual Output SPI
The W25X10A/20A/40A/80A supports Dual output operation when using the “Fast Read with Dual
Output” (3B hex) instruction. This feature allows data to be transferred from the Serial Flash memory
at twice the rate possible with the standard SPI. This instruction is ideal for quickly downloading code
from Flash to RAM upon power-up (code-shadowing) or for applications that cache code-segments to
RAM for execution. The Dual output feature simply allows the SPI input pin to also serve as an output
during this instruction. All other operations use the standard SPI interface with single output signal.
9.1.3 Hold Function
The /HOLD signal allows the W25X10A/20A/40A/80A operation to be paused while it is actively
selected (when /CS is low). The /HOLD function may be useful in cases where the SPI data and clock
signals are shared with other devices. For example, consider if the page buffer was only partially
written when a priority interrupt requires use of the SPI bus. In this case the /HOLD function can save
the state of the instruction and the data in the buffer so programming can resume where it left off once
the bus is available again.
To initiate a /HOLD condition, the device must be selected with /CS low. A /HOLD condition will
activate on the falling edge of the /HOLD signal if the CLK signal is already low. If the CLK is not
already low the /HOLD condition will activate after the next falling edge of CLK. The /HOLD condition
will terminate on the rising edge of the /HOLD signal if the CLK signal is already low. If the CLK is not
already low the /HOLD condition will terminate after the next falling edge of CLK.
During a /HOLD condition, the Serial Data Output (DO) is high impedance, and Serial Data
Input/Output (DIO) and Serial Clock (CLK) are ignored. The Chip Select (/CS) signal should be kept
active (low) for the full duration of the /HOLD operation to avoid resetting the internal logic state of the
device.
-9-
Publication Release Date: August 7, 2009
Revision F
WINBOND [ WINBOND ]
