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W25Q40BWSSIG Datasheet(PDF) 9 Page - Winbond |
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W25Q40BWSSIG Datasheet(HTML) 9 Page - Winbond |
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9 / 73 page  W25Q40BW Publication Release Date: October 11, 2013 - 9 - Revision F 7. FUNCTIONAL DESCRIPTION 7.1 SPI OPERATIONS 7.1.1 Standard SPI Instructions The W25Q40BW 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. 7.1.2 Dual SPI Instructions The W25Q40BW supports Dual SPI operation when using the “Fast Read Dual Output (3Bh)” and “Fast Read Dual I/O (BBh) ” 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 SPI 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. 7.1.3 Quad SPI Instructions The W25Q40BW supports Quad SPI operation whe n using the “Fast Read Quad Output (6Bh)”, “Fast Read Quad I/O (EBh) ”, “Word Read Quad I/O (E7h)” and “Octal Word Read Quad I/O (E3h)” instructions. These instructions allow data to be transferred to or from the device six to eight 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. 7.1.4 Hold Function For Standard SPI and Dual SPI operations, the /HOLD signal allows the W25Q40BW 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 |
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