W25Q16V
9. FUNCTIONAL DESCRIPTION
9.1
SPI OPERATIONS
9.1.1 Standard SPI Instructions
The W25Q16 is accessed through an SPI compatible bus consisting of four signals: Serial Clock (CLK),
Chip Select (/CS), Serial Data Input (DI) and Serial Data Output (DO). Standard SPI instructions use the
DI input pin to serially write instructions, addresses or data to the device on the rising edge of CLK. The
DO output pin is used to read data or status from the device on the falling edge CLK.
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 on the
falling and rising edges of /CS. For Mode 3 the CLK signal is normally high on the falling and rising
edges of /CS.
9.1.2 Dual SPI Instructions
The W25Q16 supports Dual SPI operation when using the "Fast Read Dual Output and Dual I/O" (3B
and BB hex) instructions. These instructions allow data to be transferred to or from the device at two to
three times the rate of ordinary Serial Flash devices. The Dual Read instructions are ideal for quickly
downloading code to RAM upon power-up (code-shadowing) or for executing non-speed-critical code
directly from the SPI bus (XIP). When using Dual SPI instructions the DI and DO pins become
bidirectional I/O pins: IO0 and IO1.
9.1.3 Quad SPI Instructions
The W25Q16 supports Quad SPI operation when using the "Fast Read Quad Output and Fast Read
Quad I/O" (6B and EB hex respectively). These instructions allow data to be transferred to or from the
device four to six times the rate of ordinary Serial Flash. The Quad Read instructions offer a significant
improvement in continuous and random access transfer rates allowing fast code-shadowing to RAM or
execution directly from the SPI bus (XIP). When using Quad SPI instructions the DI and DO pins
become bidirectional IO0 and IO1, and the /WP and /HOLD pins become IO2 and IO3 respectively.
Quad SPI instructions require the non-volatile Quad Enable bit (QE) in Status Register-2 to be set.
9.1.4 Hold Function
The /HOLD signal allows the W25Q16 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. The /HOLD function is only available for standard SPI and Dual SPI operation, not
during Quad SPI.
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 (DI) 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.
- 10 -
WINBOND [ WINBOND ]
